http://www.mva.maryland.gov/about-mva/info/27300/27300-28T.htm#historic said:
o be registered as a historic vehicle (class L), your vehicle must be a passenger vehicle, motorcycle or truck (with a GVWR of 10,000 pounds or less): be 20 calendar years old or older and must not have been substantially altered, remodeled or remanufactured from the manufacturers original design.
A vehicle registered as historic cannot be used for general daily transportation, or primarily for the transportation of passengers or property on highways. It can only be used in exhibitions, club activities, parades, tours, occasional transportation and similar uses. A trailer does not qualify for historic registration. They will not be used for employment, transportation to and from employment or school, or for commercial purposes.
A historic registration may also be issued to a truck with a GVWR in excess of 10,000 pounds, a tractor or a motor home as long as the vehicle is 25 calendar years old or older. The vehicle cannot be substantially altered, remodeled or remanufactured from its original design. Vehicles issued historic tags under these criteria cannot be used for occasional transportation, or for any commercial transportation of passengers or property on highways. A historic vehicle in this category must be insured by a Historic Vehicle, Show Vehicle, or Antique Vehicle insurance policy.
If your historic vehicle is 60 years old or older, you may obtain a permanent, non-transferable registration for a one-time fee. Note: A historic motor vehicle 60 years old or older do not qualify for a special registration plates since they require an annual registration fee.