License plates issued for trailers, semi-trailers, bicycles with motor attached, pole and pipe dollies and such vehicles as are exempt from the payment of registration fees under this Title shall display suitable marks or symbols, and the registration numbers assigned to each such class of vehicles shall run in a separate numerical series, except that the registration numbers assigned to such vehicles as are exempt from the payment of registration fees may run in several separate numerical series.

SOURCE: GC § 23321, enacted by P.L. 1-088 (Nov. 29, 1952).