Maryland Code, TRANSPORTATION 21-1122
(b) This section does not apply to:
(1) Authorized emergency vehicles;
(2) Vehicles operated by communications, electric, gas, or water utilities;
(3) A sound amplification system operated to request assistance or to warn of a hazardous situation; or
(4) Unless otherwise prohibited by local law, a sound amplification system used for advertising, parades, or for political or other special events.
(c) When a motor vehicle is being operated on a highway, the driver of the vehicle may not operate or permit the operation of a sound amplification system from the vehicle that can be heard outside the vehicle from 50 or more feet.
(d) A violation of this section is not considered a moving violation for purposes of § 16-402 of this article.