From personal experience I think its a bad idea. Many years ago I was out leafleting with my brother and decided to put some leaflets under car winscreen wipers on the drives to save time. turned out to be a bad idea, as when I got home i had a very angry man phone up and complain that the people who distribute my leaflets had violated his car by placing a leaflet under the winscreen wiper! The guy was really outraged and said car could have been damaged. I said sorry and would speak to leaflet people and get them to stop doing it. He was so annoyed I wasn't going to say it was me put it there on his old banger.
Phil