i had something like this happen to me. it was over a year ago, and someone threw an egg at the passenger side of my car. i didnt notice it until a day or two later, because i hardly see my passenger side exterior. tried cleaning off, but found that it chipped off some of the clearcoat! it might be keyed as well, but only very very faintly. the egg hit is clearly visible though.
pretty sure i know where/how i got it though. i had the car in santa cruz, a very liberal town, and i had a W'04 sticker on my back window, and i participated in a pro-bush rally once where i parked my car downtown for a few hours. the W'04 sticker has been slashed thorugh on my window a couple times too, only damaging the sticker. getting that angry over politics is just stupid, especially when its something as ordinary as a W'04 sticker, and it really doesnt make your side look that great when someone resorts to vandalism like this.