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. All tow truck-mounted portable variable messaging signs shall be: Permanently affixed to a tow truck; Installed at a height of at least 7 feet measured from the surface of the roadway to the bottom of the sign; and In conformance with the requirements of the MdMUTCD. A message may be displayed only while at the scene of a crash or a disabled vehicle. The message that may be displayed is “SLOW DOWN”, displayed as two lines in all upper-case letters. Any tow truck-mounted portable variable messaging sign shall only display static text that: Is colored yellow or amber, on an opaque black background; Is one consistent letter height of at least 10 inches; and Contains words within which the letter spacing is between 25 and 40 percent of the letter height. The vertical spacing between the lines of text shall be between 50 and 75 percent of the letter height. The message shall not include animation, flashing, dissolving, exploding, scrolling, or other dynamic display elements. Transportation Article, §§ 22–218(c)(7) and 22–218.2(a), Annotated Code of Maryland Effective date: March 16, 2026 (53:5 Md. R. 244)