Hmm, you know what, I take it back - it's definitely not the stock mount. It's a 2011 GSX-R600 (the insurance slip also shows 'Alstare' in the name, I can't really find any info on whether it was a special edition or if that means it has a lower-profile plate mount from the factory, though). I'll get a picture when I'm over at my folks next as it's in hibernation, but yes, I'm an idiot and never really asked the seller what was aftermarket or not. In any case, the cops who pulled me over the first time never had anything to say about it, but this guy did. Next Spring I'll see if my mechanic has any stock plate mounts lying around, because this is definitely not something I want to have to worry about again.
LOL. Well thanks again to everyone who replied.