D.C. Mun. Regs. tit. 18, r. 18-422
Whenever a motor vehicle or trailer for which District of Columbia registration is required is being operated or left standing upon any public highway, such vehicle shall display two (2) current identification tags, with one (1) on the front and the other on the rear; except as follows:
Autocycles, Motor-driven cycles, motorcycles, trailers, and vehicles identified by a dealer's tag or manufacturer's tag shall display only one (1) valid identification tag on the rear of the vehicle.
A vehicle owned by a non-resident and currently registered in another jurisdiction shall display the proper identification tag or tags issued for the vehicle in accordance with the requirements of the issuing jurisdiction; provided, that the tags are displayed in accordance with §§ 422.4, 422.5, 422.6, and 422.8.
Owner's identification tags shall at all times be securely fastened in a horizontal position to the vehicle for which they are issued so as to prevent the tags from swinging and at a height of not less than twelve inches (12 in.) from the ground, measuring from the bottom of the tags, in a place and position to be clearly visible.
Identification tags shall be maintained free from foreign materials and in a clearly legible condition. For the purposes of this subsection, foreign materials shall include any non- transparent materials placed on or over the tag(s); any expired or any unauthorized decals or stickers; or any markings or attachments of any kind, except as permitted by § 422.6.
No sign or emblem more than twenty-four square inches (24 in.2) in area shall be attached to any license tag bracket nor shall any sign or emblem be so located as to obstruct from view any part of the identification tags.
Validation stickers issued by the Director that indicate the expiration of a motor vehicle's registration period are required to be displayed as follows:
No person shall operate a vehicle where the identification tag's identifying numbers or letters are covered with glass, plastic, or any other type of material or substance.
A person operating a vehicle in violation of § 422.8 shall be subject to a fine of five hundred dollars ($ 500).
Buses owned or leased by the Washington Metropolitan Area Transit Authority or the District of Columbia Public Schools may produce and display a special tag on the rear, in lieu of a tag issued by the District of Columbia; provided, that the size, color, design, and material are approved by the Director.
D.C. Mun. Regs. tit. 18, r. 18-422