You could just require a permit to park, and permits are issued by a ticket machine, and are valid for 2 hours (or whatever). Cars without prominently displayed

You could just require a permit to park, and permits are issued by a ticket machine, and are valid for 2 hours (or whatever). Cars without prominently displayed tickets are fined, and cars with expired tickets also. Without the physical intrusion, I don't think this ruling would apply at all.