The Yahoo Search Marketing Blog announced that Google is not the only ones testing favorite icons (favicons) in the search ads. Yahoo said they are doing a limited test of favicons in the search ads in order to give their searchers one more tool to "know they’re really looking at your site, which will improve the search experience." If it increases CTR and quality score, they may expand the test and may keep it.
Here is a picture of one ad:
Forum discussion at WebmasterWorld.