AdSense blog announced that —”Starting today, you may notice some AdSense ads displaying the Google Checkout shopping cart badge alongside the ad title. These small icons identify ads that link to sites where shoppers can buy via Google Checkout. The addition of the Checkout badge makes it easier for people to find sites where they can use Google Checkout's quick, easy and secure checkout option when making a purchase.”
In addition to shopping carts on AdSense, we're also introducing new badges on ads that appear in Google search results. We hope you enjoy these new additions to our ad formats. It's another step in our ongoing efforts to enhance the experiences of AdSense publishers, AdWords advertisers, and visitors to your site.