Company registration number in your email signature: where it is required

Is a company registration number in email signature footers required? In the official texts we opened, the rules attach to business letters, invoices, official publications and similar documents, and most of them do not use the word email. One, in Mauritius, covers “any document, whether electronically or otherwise”. Many countries have no source we found at all. This is general information, not legal advice, and we read every page named here on 4 October 2026.

So the careful reading is that a company registration number in email signature footers is, in most places we checked, a decision to make with an adviser and not a duty we can point to. The table below shows each place, the source and what it says, so you can see where the gaps are.

Company registration number in email signature rules by country

Place	Source we opened	What it requires	Does it name email?
United Kingdom	GOV.UK and 2015 Regulations, Part 6 (primary)	Registered number, registered office address and place of registration on business letters, order forms and websites; registered name on wider correspondence	No
South Africa	Companies Act 71 of 2008, s.32(4) via Acts Online (secondary)	Name and registration number in notices, official publications and letters, invoices and similar	No
Mauritius	Business Registration Act 2002, s.14 (primary)	Business registration number on documents used in a transaction, “whether electronically or otherwise”	Not by name, but covers electronic documents
OHADA states	Uniform Act on commercial companies, 2014 revision, art. 17 (copy of the text)	Company name with legal form, capital, registered address and trade register number on documents sent to third parties	No
Nigeria	Adeola Oyinlade, 9 July 2026 (secondary, law firm)	Registration number on business correspondence, as described by the firm; CAC site not opened	Not in the summary we read

The United Kingdom

For a company registration number in email signature footers, the UK has the clearest paper trail. GOV.UK’s guidance for limited companies says: “You must include your company’s name on all company documents, publicity and letters.” It then lists what business letters, order forms and websites must show: the registered company number, the registered office address, where the company is registered (England and Wales, Scotland or Northern Ireland) and that it is a limited company. Email is not mentioned on the page.

The Company, Limited Liability Partnership and Business (Names and Trading Disclosures) Regulations 2015 give the legal text, and we opened three provisions. Regulation 25(1) says every company shall disclose the particulars in paragraph (2) on its business letters, its order forms and its websites. The particulars include the part of the UK of registration, “the company’s registered number” and “the address of the company’s registered office”.

Regulation 24(1)(g) asks for the registered name on “all other forms of its business correspondence and documentation”. Regulation 29(c) says a reference to a type of document means one “in hard copy, electronic or any other form”.

Put together: an electronic business letter is still a business letter. Whether a given email is one is a judgement we cannot make for you, and our UK business email legal requirements article works through it. Companies often add the full set to every external email because it costs little.

One rule does name e-mails. The Solicitors Regulation Authority’s Transparency Rules, rule 4.2, say an authorised body’s “letterhead and e-mails must show its SRA authorisation number and the words ‘authorised and regulated by the Solicitors Regulation Authority’”. We read the version in effect from 11 April 2025. It applies to SRA authorised bodies, and the number it names is the SRA’s, not the one on the company register.

South Africa

The South African rule on a company registration number in email signature footers is old wording applied to a new medium. Acts Online is a private legal publisher, so we class its text as secondary.

Section 32(4) of the Companies Act, as shown there, says every company “must have its name and registration number mentioned in legible characters in all notices and other official publications of the company, including such notices and publications in electronic format as contemplated in the Electronic Communications and Transactions Act, and in all bills of exchange, promissory notes, cheques and orders for money or goods and in all letters, delivery notes, invoices, receipts and letters of credit of the company”. Section 32(5) says contravention of subsection (4) is an offence.

Notice the structure. “Electronic format” is tied to notices and official publications. Email is not named, and “letters” is a different word. We cannot tell you whether a business email is a letter for this purpose.

Section 43 of the Electronic Communications and Transactions Act, also from Acts Online, asks a supplier selling by electronic transaction to show a registration number on its website. That covers websites, not email footers. The company registry’s own page, CIPC, told us only that a company registered without a reserved name uses its registration number as its name, with “(South Africa)” added. Our page on POPIA and email covers a different rule about marketing.

Mauritius

Mauritius is the nearest we found to a rule that fits a company registration number in email signature use. The Business Registration Act 2002, on the Registrar’s site in a consolidated PDF named for 31 August 2026, has section 14. It says that “every person registered under this Act shall, in respect of every transaction he makes, use and indicate on any document, whether electronically or otherwise” the person’s business registration number, and the other party’s number where that party is registered under the Act. Subsection (2) says failing to comply is an offence with a fine not exceeding 100,000 rupees.

Section 6 says nobody shall carry on business in Mauritius unless registered under the Act, and the Act defines “company” as one incorporated or registered under the Companies Act 2001. We did not work out how the Act and the Companies Act interact, so ask a local adviser which regime your business sits under. The text does not name email or signatures, and whether an email is a “document used in a transaction” is for a local adviser.

OHADA states

For a company registration number in email signature footers across OHADA states, the starting point is one article. The Uniform Act on commercial companies and economic interest groups, revised on 30 January 2014, applies to any commercial company whose registered office is in a State party to the OHADA Treaty (article 1).

Article 17 says, in French, that the company name must appear on “tous les actes et documents émanant de la société et destinés aux tiers, notamment les lettres, les factures, les annonces et publications diverses”, and that the name must be preceded or followed, in legible characters, by the company’s form, share capital, registered address and “numéro d’immatriculation au registre du commerce et du crédit mobilier”. In our words: documents sent to third parties, including letters, invoices and announcements, must show those details. The word email does not appear in that article.

Our copy is a reproduction hosted on a government justice site (justice.gouv.km), carrying the droit-afrique.com banner, so we cannot call it the official gazette text. We did not check later revisions. Check the current text with a local lawyer.

Nigeria

The Nigerian position on a company registration number in email signature footers is the least certain of the five. We cannot open the CAC’s own pages, which returned an access error.

What we have is secondary: a law firm’s alert, dated 9 July 2026 on its page, saying the CAC will enforce sections of CAMA 2020 on business correspondence from 1 August 2026, and listing the company name as registered and the RC number among the details. The summary lists letterheads, invoices, quotations, proposals, tenders and official business correspondence, and email did not appear in that list. We could not confirm whether the CAC treats an email as a business letter. Our full write-up is the CAC business letter requirements email article, which keeps the same caveat.

Where we found nothing on a company registration number in email signature

For the United States, Canada and most other countries, we did not find an opened official source requiring a company registration number in email signature footers. We found rules in other areas, such as sender identification in marketing email, but that is not the same thing. If you operate in one of those countries, ask your accountant or registry, and do not treat our silence as a rule either way.

Writing a company registration number in email signature footers

If you decide to include a company registration number in email signature footers, use the label your own register uses, and copy the value from the register. The made-up examples below show two styles.

Harbour Studio Limited is registered in England and Wales. Company number: 01234567. Registered office: 10 Example Street, London EC1A 1AA.

That follows the particulars in regulation 25(2). The company and number are made up. Here it is in a drawn signature:

A classic layout with a company details footer. The company, number and person are made up.

For Mauritius, a company registration number in email signature text might read as the next example, with a placeholder where your own number goes:

An aligned layout with a registration line. The company and person are made up.

Keeping the company registration number in email signature footers right

• Copy it, do not retype it. Take the number and the registered name from your register entry. A typo repeats on every email.
• Use the registered name. The UK regulation asks for the registered name, which may differ from your trading name.
• Assign an owner. Registered office moves and name changes make the footer wrong on every message until someone updates it. Our page on the address in an email signature covers the address side.
• Lock it. A company registration number in email signature text that depends on each person typing it will be missing on some messages. A tool such as emailfooter lets the company admin set a footer line once for the company’s signatures. Employees install their own by following steps, and nothing is pushed into mailboxes.
• Keep other notices separate. Confidentiality and privacy lines are a different job. See the email disclaimer examples.

If the rule is unclear where you work, treat the company registration number in email signature footers as a small, low-cost precaution and a decision for your adviser, not as proof that the law demands it. Check the register entry, fix the wording once, and keep it current.

Frequently asked questions

Do I need a company registration number in email signature footers?

In the sources we opened, the duties name business letters, invoices, official publications and similar documents. Only the Mauritius text covers any document electronically. Ask an adviser whether your emails count.

Is a registered office in an email footer required?

In the UK, regulation 25 asks for the registered office address on business letters, order forms and websites, and does not name email. Many companies add it to external email as a precaution. That is a choice, not a duty we found stated.

What is the difference between a company number in email and a VAT number?

They are different identifiers. The UK and South African texts above ask for the registration or company number, and we did not read tax-number rules.

Does a sole trader need to show a number?

The GOV.UK page we read is for limited companies, and we did not read rules for other business types. Check with your registry or an adviser.

Which countries require a company registration number in email signature footers?

We found no opened source that says so in plain terms for any of them. Mauritius comes closest with its wording on documents used in a transaction, “whether electronically or otherwise”.