Stuck under the windshield wiper, a strip of cardboard from a cigarette carton becomes a proof of payment for parking in this open space next to a busy street. How is this system vulnerable to manipulation? Could one look around and, if the parking attendant happens not to be looking, figure out what the marker of payment is and "rip one off" (either figuratively with a quick improvised slip, or literally - from another vehicle's windshield)? Could the parking attendant defray risk of being cheated by routinely switching up the type/color/brand of carton? Switching the used recycled/found permission-granting materials entirely?