Md. Code Ann., Bus. Reg. § 9A-404

Each advertisement for heating, ventilation, air-conditioning, or refrigeration services that is in the name of a person who provides heating, ventilation, air-conditioning, or refrigeration services shall contain the license number and name of a master, master restricted, or limited license holder whom the person employs and designates to direct and control the provision of heating, ventilation, air-conditioning, or refrigeration services through the business of the person.