All platforms with Firefox: The WiseStamp beta Firefox add-on edits, saves, and applies rich HTML signatures to your web-based email accounts, including Gmail, Yahoo Mail, Hotmail, and AOL mail. With WiseStamp installed, you get a rich HTML editor that lets you create signatures with links, colours, images, and formatting, plus links to your favourite social network profiles. You can make more than one signature, too—like personal and business. Once you're in your webmail account, WiseStamp adds a signature drop-down so you can choose which sig to use with the current email, or it can insert it automatically. Take a look at some screenshots of WiseStamp in action.
Launch WiseStamp's preferences pane to start creating your signatures.
By default WiseStamp includes a small WiseStamp advertisement at the bottom of your signature. You can disable that, as well as the "Contact Me" text in the settings area.
Here's what the WiseStamp signature I made looks like in Gmail:
Judging from the demand for HTML signatures in Gmail, looks like WiseStamp will make quite a few people happy. Our most-wanted feature for WiseStamp? Syncing signatures across computers. WiseStamp is a free download, works with and wherever Firefox does.