I'm investigating legally of motor driven bicycles and I came across this in PA's Title 75 Vehicle Code; Chapter 11 § 1102. Vehicles not requiring certificate of title. No certificate of title is required for: (1) A vehicle owned by the United States unless it is registered in this Commonwealth. (2) A golf cart, motor-driven cycle, go-cart or other similar vehicle unless it is registered in this Commonwealth. And then this; Chapter 13 § 1301. Registration and certificate of title required. c. Certificate of title prerequisite to registration.--No vehicle shall be registered unless a certificate of title has been applied for or issued if one is required by Chapter 11 (relating to certificate of title and security interests). I think there would be a good case for saying, "If you are not required to title your bike, you're exempt from registration". I haven't tested it in court but it seems clear that either the law contridicts itself or there is not need to jump through the hoops PA expects you to. And then there are the police who are sometimes ignorant of the laws they try to enforce.