Motor vehicles, trailers, and semitrailers owned by the Commonwealth and the counties, cities, and towns thereof and used solely for police work may be issued the same license plates as those issued in registration of vehicles owned by private citizens. The head of a state agency, the chief of police of a city, county, or town having a police department, or the sheriff of a city or county, shall certify under oath and the law-enforcement agencies of the federal government shall certify to the Commissioner of Motor Vehicles the vehicles to be used solely for police work.