Google seems to be testing yet a slightly different format for their arrows on their AdSense ad units.

A WebmasterWorld thread has one user who posted a picture of an AdSense unit that had an arrow that looked slightly 3D or shadowed, with the look that you can press on it as a real button.

Here is a picture of a standard AdSense ad with a normal arrow:

Here is the screen shot shared in WebmasterWorld of the 3D like button:

The AdSense publisher felt it directly impacted his AdSense earnings in a positive way, he said:

Forum discussion at WebmasterWorld.