Maryland Code, Transportation § 21-205

(a) A person may not place, maintain, or display on or in view of any highway any unauthorized sign, signal, marking, or device that purports to be, is an imitation of, or resembles a traffic control device or a railroad sign or signal.

(b) A person may not place, maintain, or display on or in view of any highway any unauthorized sign, signal, marking, or device that attempts to direct the movement of traffic.

(c) A person may not place, maintain, or display on or in view of any highway any unauthorized sign, signal, marking, or device that hides or interferes with the effectiveness of a traffic control device or a railroad sign or signal.

(d) A person may not place, maintain, or display on or in view of any highway any unauthorized sign, signal, marking, or device that, except as otherwise permitted by law, contains:

(e) A person may not place or maintain on any highway nor may any public authority permit on any highway any traffic sign or signal that has any commercial advertising on it.

(f) This section does not prohibit the placement on private property adjacent to a highway of a sign giving useful directional information, if the sign is of a type that cannot be mistaken for an official sign and is placed with the approval of the State Highway Administration.

(g) Each sign, signal, marking, or device prohibited by this section is a public nuisance, and the authority that has jurisdiction over the highway may remove it without notice.