D.C. Mun. Regs. tit. 17, r. 17-214
Each contractor bonded and licensed to engage in a business under this chapter shall display the license in a frame under a glass in a conspicuous place accessible for inspection in the location specified on the license.
Occupational licenses issued in the form of a card shall be carried on the person of the licensee.
It shall be unlawful for any person to display a sign stating or implying that he or she is conducting a business requiring a license under this chapter; or to advertise by means of business cards, stationery, or any publication, or directory; or to claim orally to a prospective customer; or otherwise to indicate that he or she is conducting such a business, unless he or she is licensed to do so as provided in this chapter.
Contractors licensed under this chapter who have no regularly established place of business in the District shall establish a local office in the District at which the appropriate licenses shall be displayed and where legal notices may be served.
If a contractor is a non-resident of the District, or has designated on his or her license application a local officer of the firm or corporation who is a non-resident of the District, the contractor shall also designate by name and address an individual who is a resident of the District and who, by a signed statement, agrees to be the local representative of the contractor to accept notices, summons, or other legal notices for that contractor and to notify the Director of any change in his or her address or any change in the conditions of the agreement to act as agent for the contractor.
D.C. Mun. Regs. tit. 17, r. 17-214