In this chapter, the following terms have the meanings indicated. Terms Defined: “MdMUTCD” means the Maryland Manual on Uniform Traffic Control Devices for Streets and Highways adopted in Transportation Article, §25-104, Annotated Code of Maryland. “Portable variable messaging sign”, also referred to as a “portable changeable message sign” in the MdMUTCD, means a sign that is capable of displaying more than one message, of which one message may be a blank display, and that is changeable manually, by remote control, or by automatic control. “Tow truck” has the meaning stated in Transportation Article, §13-920, Annotated Code of Maryland.