Idk about your area, but up in alaska it is mandatory that the owner be notified 24 hours before towing, whether that be a sign at parking or a written ticket on the windshield. The APD don't really do anything until someone complains about a car and after the complaint, they sit on it for like 2 or 3 days before doing anything.
Was it in a public lot? If its a private lot, then I would talk to the owner, they are usually the ones that responsible to have a car towed off their lot. I've read a article of a guy that had his car towed (not repo'd) on a private lot without the lot owners permission and went to court and won agaist the local PD. The lot owner is the one that has to file the suit though.
Might want to look into the policy in your area.