Maryland Code, Transportation § 25-105

(a) On every highway under its jurisdiction, the State Highway Administration shall place and maintain those traffic control devices that it considers necessary to carry out the provisions of the Maryland Vehicle Law  1 or to regulate, warn, or guide traffic. Each of these traffic control devices shall conform to the manual and specifications of the State Highway Administration.

(b) A local authority may place or maintain a traffic control device on a highway under the jurisdiction of the State Highway Administration only with the permission and under the direction of the State Highway Administration.