Not condoning, but here's a (naive?) though experiment if the Barnacle shows up in use again... Park your car and cover it. Many car covers have cable locks to prevent removal and openings to expose plates for legal/bylaw reasons, so this should be permissible. This may provide protection from sun, frost, birdshit, and now Barnacles(tm)! My assumption is that parking enforcers don't have permission to modify, remove, or damage property on a parked car like this.
Of course, there's always a tow-truck. Or you could pay for the parking you use, but I respect the hacker spirit!