Google recently changed the format for the arrows on AdSense ads to be a thin arrow on a block background color. Google is constantly messing with the AdSense design in order to keep click-through-rates higher on those ads.
The next test being reported is extremely wide arrows on AdSense units. I am personally not able to replicate it but there is a discussion going on in WebmasterWorld with two different Google publishers noticing it. One posted a screen shot of the ad, but blurred it out, so it is a bit hard to make out.
Here is that screen shot:
It is unclear if this is a test, bug or the real deal.
Forum discussion at WebmasterWorld.