Gmail the mostly used Email service by all people. But it has one small disadvantage that Gmail does not allow to insert HTML Signatures inside settings. This small disadvantage is solved by using an Firefox Add on Blank Canvas Gmail Signatures.

Install Firefox Add on Blank Canvas Gmail Signatures on your Firefox browser, perhaps to install Blank Canvas Gmail Signature Add on you need to sign up for Firefox Add On.

After installing restart your Firefox browser and move to Compose Mail in your Gmail account.

You can see a drop down box near From address which contains list of template names like Default, Friends, Family and Business in that select any option and create signatures as shown in above figure.

Insert HTML code in first box you can get preview in second box and save it. Every time when you send mail just select the template it will automatically insert HTML signature in your Compose Mail.

More Information and Starting Guide for Blank Canvas Gmail Signature.