Google +1 Button on AdSense Ads
Is it a addition to their Google +1 development or to AdSense? whatever, but the idea is that more relevant ads should appear on your site. So if you click on +1 button on a AdSense display ad it means it’s a vote to that ad and you are endorsing it to appear to your social connections.
Google explain it further;
Starting in October, the +1 button will begin to appear on display ads on your site. With a single click, people will now be able to endorse specific ads and make them more likely to appear to their social connections. We believe that these recommendations could lead your readers to notice ads on your site more, leading to more clicks and higher returns for you over time.
A click on +1 button would not generate any revenue, though Google believes it will somehow increase your earning potential, as the ads appearing on your site will also show up images of your friends who have recommended it. It will make display ads and AdSense for content ads powerful resulting is a better advertising experience and ultimately making a higher returns.
The +1 button will begin to appear on AdSense for content and AdSense for mobile content display ad formats–image, animated gif, and Flash ads. If you’d prefer not to allow the use of +1 features and social annotations on display ads on your pages, you can opt out starting today by signing in to your account at google.com/adsense.
The +1 button and recommendations will appear at the bottom of display ads