Md. Code, Pub. Safety § 5-102

This subtitle does not apply to: (1) the transfer or possession of a regulated firearm or detachable magazine: (i) for testing or experimentation authorized by the Secretary; and (ii) by a federally licensed gun manufacturer, dealer, or importer; (2) the sale, transfer, or possession of an antique firearm; (3) an unserviceable firearm sold, transferred, or possessed as a curio or museum piece; (4) law enforcement personnel of any unit of the federal government, members of the armed forces or the National Guard, or law enforcement personnel of the State or any local agency in the State, while those personnel or members are acting within the scope of their official duties; (5) a regulated firearm modified to render it permanently inoperative; (6) purchases, sales, and transportation to or by a federally licensed gun manufacturer, dealer, or importer; (7) an organization that is required or authorized by federal law governing its specific business or activity to maintain firearms; (8) the receipt of a regulated firearm by inheritance, if the heir forwards to the Secretary a completed application to purchase or transfer that regulated firearm; or (9) a signal pistol or other visual distress signal that the United States Coast Guard approves as a marine safety device.