You should not sticker people's cars. It would be much better to put it under their windshield wiper like an advertising flyer. This will give them the opportunity to consider how their behavior impacts others. If you're trying to educate someone, your first step should not be doing something that enrages them.
Furthermore, you don't suddenly gain the right to vandalize people's property because they are acting insensitive to the needs of others or in violation of the law.