I have 4 of these things... 2 came with the CAI, and 2 came with the exhaust. I was originally going to put one on both rear windows, way down at the bottom... but then I decided not to at all, because I want to keep a clean look, and not mis-represent my car either.
I do however, want to get a mazda3forums sticker and put it on the front window, down towards the right bottom of the windshield. There is one person here on the forums that has it set up like that, and its not distracting. It looks clean. The thing with stickers is that people sometimes go overboard, and it just looks plain funny.