I have been a commuter here in Minneapolis now for a number of years and have had hundreds of incidents involving idiot and uninformed drivers trying to swerve at me or run me off the road.
After much thought I have come up with a way to let them know they are in the wrong and maybe even get them to think twice about doing it next time - without any nasty confrontations...
I did know a guy who had photocopies of Mickey Mouse flicking the bird and a voice bubble saying much the same, but way more abusive. He used to put them under the offending vehicles windscreen wipers at the lights. I like your idea as it is much less confrontational. Some used to try and run the guy I knew over, either as he was placing them, or more often, shortly after reading them...😠
I'm currently considering getting a VeeCam and putting the resulting video clips up on YouTube or collating them into a video with a suitable comedy score/voice overs. Revenge is a dish best served cold.🙂