Md. Code, Bus. Reg. § 9A-401

(a) Each licensed master, master restricted, or limited heating, ventilation, air–conditioning, and refrigeration contractor shall display: (1) the license and the license number conspicuously in the principal place of business of the licensee; and (2) the license number of the licensee on each vehicle used on the job for providing heating, ventilation, air–conditioning, or refrigeration services. (b) (1) Except as provided in paragraph (2) of this subsection, a county or municipal corporation may not require a person licensed under this subtitle to display a county or municipal corporation certificate number on each vehicle used on the job for providing heating, ventilation, air–conditioning, and refrigeration services. (2) This subsection does not apply to Anne Arundel County. (c) Each licensee shall give the Board written notice of any change of name, address, or employment from that which appears on the current license, at least 10 working days before the change is to take effect.