Sankar Anand, a regular reader of this blog, noticed a strange AdSense ad on his site.On top of the text ads, there is a small image, unrelated to the subject of the ads, that just wants some attention. This seems to be an experiment made to increase the visibility of the ads.
Google allows webmasters to put images above AdSense ads as long as there is a border that demarcates the images.
You can see the whole ad if you click on the image.
Related:
Video AdSense
Pay-Per-Action AdSense