D.C. Code § 22-4512

No person shall within the District of Columbia change, alter, remove, or obliterate the name of the maker, model, manufacturer’s number, or other mark or identification on any pistol, machine gun, or sawed-off shotgun. Possession of any pistol, machine gun, or sawed-off shotgun upon which any such mark shall have been changed, altered, removed, or obliterated shall be prima facie evidence that the possessor has changed, altered, removed, or obliterated the same within the District of Columbia; provided, however, that nothing contained in this section shall apply to any officer or agent of any of the departments of the United States or the District of Columbia engaged in experimental work.