If you send a lot of emails in a day, you can save time by using a preset signature. When you send an email from an account that has a signature, the signature will automatically appear at the end of each email. Learn how to set up a basic rich text email signature with iOS 10 or later.
How do I add an email signature on iPhone?
To add a basic signature (including bold, italic, and underline formatting) to the text of your iOS Mail email signature:
From the Home screen, open the Settings app.
Scroll down and select Mail.