A couple of weeks ago, Rosa Golijan posted a tip in Lifehacker, wherein, she mentioned a few sentences using which as Email signature massacred the Gmail ads automatically. Though it was a quite interesting tip, but it is not always practical to use an irrelevant signature on your email so that the receiver of the email may not see those distracting ads within Gmail.
You can remove such unwanted ads from your webmail service (Gmail, yahoo, etc) simply by installing a Firefox add-on – Webmail ad blocker and forget those ads forever. 😉
Screenshot:
Ads visible without Firefox addon – WebMail Ad Blocker
Ads are massacred completely only with a Firefox add-on! 
Links: Download Firefox Web browser | Download WebMail ad Blocker add-on for Firefox