I remember seeing recently on one of those Police Interceptors/Polica Camera Action type programmes, a guy waiting to fill up a a petrol station. Police car pulls into same garage to full up & one of the officers just happened to noticed that this guy's reg plate looked funny in one of their cameras. It was because it was sprayed with that stuff. If he hadn't tried to be sneaky & spray it, the Police wouldn't have taken a blind bit of notice to him. Made me chuckle.