Md. Code, Transportation § 8–736

(a) The political subdivisions of this State have full authority, under their respective zoning powers:

(1) To zone areas for commercial or industrial purposes; and

(2) In these areas, to govern the size, spacing, and lighting of outdoor signs.

(b) Notwithstanding any provision of this part or any rule or regulation of the Administration:

(1) Local zoning regulations that relate to outdoor signs in commercial or industrial areas shall govern within the zoned area; and

(2) If a political subdivision adopts comprehensive zoning that includes the regulation of outdoor signs:

(i) The Administration may so certify to the Federal Highway Administrator; and

(ii) On certification, the control of outdoor signs in commercial or industrial areas transfers to the political subdivision.