17 Del. C. § 147

(a) The Department shall adopt a uniform standard for each type of traffic-control device to be used on all highways open to the public in this State. Such standard shall correlate with, and so far as practical, conform to the standards used in other states, except that the Department is authorized to adopt different standards and types of devices or applications if the Department determines that, based on engineering judgment, different standards or types of devices or applications are needed in order to reduce fatal or serious injury crashes or improve safety in accordance with a “safe system approach,” as defined under § 135A of this title. For purposes of this subsection, “standards” includes publications, policies, guidelines, or memoranda.

(b) The standards shall be recorded in a manual to be known as the Delaware Manual on Uniform Traffic-Control Devices for Streets and Highways. The manual shall have separate chapters setting individual standards for signs, signals and markings.

(c) Any traffic-control device erected in violation of the manual, except experimental devices erected by the Department, shall be unofficial, unauthorized and unenforceable.

(d) A person or corporation shall not sell or offer for sale in this State any traffic-control device or other device intended to regulate, warn or guide traffic unless it conforms with the state manual and specifications adopted under this section.