Rich text signatures have now been added to Gmail allowing you to add your own formatting, images and links to your email signatures. If you have configured your Gmail account to also send mail using the Send mail as/custom ‘from’ feature, then you can now also have a unique signature for each these other addresses that you’ve added to your account.

Editions included:
Standard, Premier, Education and Partner Editions

Languages included:
All languages supported by Gmail

How to access what's new:
In your Gmail account, go to ‘Settings’ then the ‘General’ tab. The new rich text editor is in the signature section. Edit the formatting for your signature as you would like it to appear on all outgoing messages and click ‘Save changes’.

For more information:
http://gmailblog.blogspot.com/2010/07/rich-text-signatures.html
http://mail.google.com/support/bin/answer.py?hl=en&answer=22370