Maryland Code, Transportation § 13-409

(a) An individual who is driving or in control of a vehicle shall carry a registration card in the vehicle to which the registration card refers.

(b) On demand of a police officer who identifies himself as a police officer, an individual who is driving or in control of a vehicle shall display a registration card that refers to the vehicle.

(c) An individual may satisfy subsection (a) or (b) of this section by carrying in the vehicle and making available a valid rental agreement in place of a registration card in the case of a rental vehicle that is:

(d) This section does not apply if the card is being used to apply for the transfer of registration of the vehicle.