Open Gmail
Click the gear icon (Settings)
Select “See all settings”
Scroll to “Signature”
Choose the email account (if you have multiple)
Create or edit your signature in the box
Use formatting options as needed
Check “Insert this signature before the quoted text in replies and remove the separator line” (optional)
Check “Create new emails” and/or “For replies or forwarding” to apply the signature
Click “Save Changes”