From the Google AdSense team…
In the next month, we’ll introduce the +1 button and personal recommendations to display ads. The +1 button will begin to appear on AdSense for Content and AdSense for Mobile Content display ad formats — image, animated gif, and Flash. +1s will be one additional signal to help determine an ad’s relevance and we’ll continue to show the ads that will generate the most revenue for you.
We previously launched the +1 button on Google search and for publisher sites to make it easier for people to share and discover content across the web. Soon, your users will be able to endorse specific ads and make the ads more likely to appear to their social connections. We believe that these recommendations could help your readers notice ads on your site more, leading to higher returns for you over time.
If you prefer not to show the +1 buttons on display ads on your pages, you can opt out in your account. For more information please visit the Inside AdSense blog.
Sincerely,
The Google AdSense team