How do I add a email signature to Gmail Mail ?

1- Select the email signature using your cursor and copy it to your clipboard.

Open your Gmail inbox and go to your preferences, then the signature section, then paste your email signature from the clipboard.

Once done, press the save button at the bottom of the settings window and your email signature should now be showing on your new emails.

Create a new email and voila: your new email signature should be there.

Gmail limits signatures to 10,000 characters.

There are two instances where you could reach that limit:
-If your signature has a very long disclaimer
-If your signature has over 10 social icons.
Keep in mind the HTML code behind your signature is very long and complex.