I used to have a license plate with "ROCKNE" on it and never once during the 10 years it shifted from car to car did any SC fans disturb it when I took it to the Coliseum.
Strange that they would pick on your car - and a rental to boot.
Why do you think they chose your car? Did they damage any others? Truly a case of malicious mischief if I have ever heard of one - which I have.
I'm not sure my car was chosen for any other reason than it was in close proximity to the DJ's table. The other cars/trucks around me suffered as well. It was a pretty raucous event.