There's a local LBS that keeps a list of plate numbers from aggressive and hostile drivers that local cyclists report. I did a jersey design for them a few years back and they actually wanted me to list the plate numbers on the back of the jersey! This was so that when riding in a group the person behind could read the plates. While kind of funny, I did not think that was appropriate and would only increase hostility between cyclists and drivers. Anyways, they keep the list and report it to the authorities. This way they can keep track of repeated offenders.