And I thought reading through Maryland law gave me a freaking headache...Although I do not have anything registered in D.C., your question got me thinking, so I did some digging.
District of Columbia Official Code 2001 Edition
Division I. Government of District.
Title 7. Human Health Care and Safety. (Refs & Annos)
Subtitle J. Public Safety.
Chapter 25. Firearms Control.
Unit A. Firearms Control Regulations.
Subchapter II. Firearms and Destructive Devices.
§ 7-2502.03. Qualifications for registration; information required for registration.
I didn't see anything in the above D.C. law "qualification for registration"stating that residency of the District was a requirement for registration. I would say that the registration process is intended for firearms stored within the borders of the District. For merely transporting afirearm through D.C., see the quote below from DC ST § 7-2502.01:
"With respect to firearms, any nonresident of the District participating in any lawful recreational firearm-related activity in the District, or on his way to or from such activity in another jurisdiction; provided, that such person, whenever in possession of a firearm, shall upon demand of any member of the Metropolitan Police Department, or other bona fide law enforcement officer, exhibit proof that he is on his way to or from such activity, and that his possession or control of such firearm is lawful in the jurisdiction in which he resides; provided further, that such weapon shall be unloaded, securely wrapped, and carried in open view."
How can a firearm be securely wrapped and carried in plain view...plastic wrap?
Link used to D.C. law:
Oh yeah, and I'm not a lawyer...If you looking for an authoritive answer, I would recommend calling or emailing the registration authority, the MPD Chief. Maybe the registration question for D.C. will be answered soon by the Supreme Court