To set up a signature automatically added to emails you compose in Gmail, follow these steps:

Step 1: Click the Settings gear in your Gmail toolbar

Step 2: Under Setting page, find Signature section and make sure do not choose No signature. At the text editor you can make your signature by yourself by: type text, insert images,… If you want to move your signature above quoted text in replies, click to Insert this signature before quoted text in replies and remove the “–” line that precedes it.

Step 3: Click Save Changes button at the bottom of Setting page

Now your gmail will insert the signature automatically when you compose a message. And also you can edit or remove it before clicking Send.