Add or change a signature Estimated reading: 1 minute 0 views Add or change a signature You can put up to 10,000 characters in your signature. Open Gmail. In the top right, click Settings See all settings. In the “Signature” section, insert your image signature by clicking on the image icon in the text editor. Once image uploaded completely, click on the image and set the Large size. At the bottom of the page, click Save Changes.