D.C. Mun. Regs. tit. 19 § 1201
No person shall offer to act as a sightseeing tour guide on the roads, sidewalks, public spaces, or waterways of the District of Columbia unless the person holds a valid sightseeing tour guide license issued by the Department of Consumer and Regulatory Affairs (Department).
No sightseeing tour guide shall engage in business or do business with a company or individual not properly licensed by the Department as a sightseeing tour company, if required by District law.
No business or entity shall offer, for a fee, to conduct walking tours or tours where customers operate self-balancing personal transport vehicles, mopeds, or bicycles unless the business or entity is licensed by the Department as a sightseeing tour company.
No person other than a licensed sightseeing tour guide shall, by the use of a uniform or part of a uniform, or by the use of insignia, device, word or words, or sign, indicate that he or she is engaged in the business of furnishing a sightseeing tour guide service, either on his or her own behalf or on behalf of another.
No person, other than a licensed sightseeing tour company or sightseeing tour guide may use the words "sightseeing," "tours," "guide," or any combination of these words, to advertise the availability of sightseeing tour services. This prohibition shall not apply to the use of these words as part of the identifying lettering on vehicles coming into the District or to a tour that is not conducted for profit or compensation.
D.C. Mun. Regs. Tit. 19, § 1201