A couple ofyears ago, when I first moved to GMAIL, I wrote a blog (how to display images in Google mail). Things have changed massively since then, not least being the introduction of email .sigs in GMAIL itself. But, nowadays I get so much email fluff I have just decided to split my email into two accounts: GoogleMail for personal stuff and Office365 for business.
So I now have two seperate email sigs...
Personal email -- FACEBOOK Image in gmail signature
Now, with a basic knowledge of HTML you can edit the source code to include any extra bits you wish.
I have a much more boring business email signature. So, when sending mails from my *work* account I simply use images pulled from the business server @ projex.com