1. 1Press "Copy signature" above.
2. 2In Gmail on a computer, open Settings (the gear at the top right) and choose See all settings.
3. 3Scroll down to Signature and choose Create new. Give the signature a name.
4. 4Click in the signature box and paste (Ctrl+V, or Cmd+V on a Mac).
5. 5Choose when to use it, then press Save Changes at the bottom of the page.

Gmail allows up to 10,000 characters in a signature, and an image counts toward that limit. Gmail's help suggests images about 70 to 100 pixels high and 300 to 400 pixels wide. An image kept on Google Drive shows only if its sharing is set to public.

Source: Gmail Help: create a signature

1. 1Press "Copy signature" above.
2. 2In new Outlook, open Settings, then Accounts, then Signatures.
3. 3Choose Add signature and give it a name.
4. 4Click in the box and paste.
5. 5Tick whether it goes on new messages and on replies and forwards, then press Save.

To add it to one email by hand, open New mail, then Insert, then Signature.

Source: Microsoft Support: create a signature in Outlook

1. 1Press "Copy signature" above.
2. 2In classic Outlook for Windows, open File, then Options, then Mail, then Signatures.
3. 3Choose New and type a name for the signature.
4. 4Right-click in the Edit signature box and choose Paste.
5. 5Choose it for new messages and for replies and forwards, then press Save and OK.

Classic Outlook keeps these signatures on the computer where you made them, so set it up again on another computer. Microsoft lists a fixed known issue in which Version 2512 added table borders to signatures: if you see lines around yours, restart classic Outlook to get the fix.

Source: Microsoft Support: add and change a signature

1. 1Press "Copy signature" above.
2. 2In Mail on your Mac, choose Mail, then Settings (Preferences on older macOS), then Signatures.
3. 3Choose your account, click the Add button and type a name.
4. 4Turn off "Always match my default message font", so the signature keeps its own font.
5. 5Click in the preview area and paste. Then pick it in the Choose Signature menu for that account.

Apple Mail can place the signature above or below the quoted text of replies: see "Place signature above quoted text".

Source: Apple Support: email signatures in Mail on Mac