Maryland law states --
"Section 22-206(a)(1): Every motor vehicle registered in this State and sold as a new vehicle after June 1, 1967, shall be equipped with at least two stop lamps."
In the section on brake lights, there is no mention of a requirement for a third operable brake light.
But then... there is the Code of Maryland Regulations...These deal with the inspection of vehicles in Maryland. These regulations state that in order for a vehicle manufactured after 1985 to pass inspection, there must be a center operable brake light in addition to the side brake lights.