Over eight years ago, Google AdSense tested showing favicons in AdSense ads - little graphics next to the title of the AdSense ad unit. Now it seems Google is testing it yet again.
A WebmasterWorld thread has a couple publishers noticing this. In fact, one posted a picture of this in action.
This time, instead of the favicon being next to the title, it is next to the URL. Here is a screen capture:
I personally did not see this but it wouldn't surprise me if Google is testing this.
Forum discussion at WebmasterWorld.