Open Gmail and sign in to your account
Click the gear icon in the top right
Select See all settings
In the General tab, scroll to the Signature section
Click Create new or select an existing signature to edit
Enter or update your signature text
Format the signature if needed
Scroll down and click Save Changes
To choose a default signature, use the dropdowns in the Signature section before saving
To change your signature on mobile, open the Gmail app, tap the menu, go to Settings, select your account, and update the signature if available