Md. Code, Transportation § 8–728

A person may not use his property or allow his property to be used by any other person for the erection or maintenance of any outdoor sign along or near any federal-aid primary highway, unless:

(1) The sign is in a commercial or industrial area; or

(2) The sign is:

(i) In an urban area; and

(ii) More than 660 feet from the nearest edge of the right-of-way of the highway.