Here's the answer from the D.C. folks on the flare gun issue:
This email is in response to your question about carrying a flare gun in D.C. waters. According to D.C. code a flare gun used as a safety device is not considered a handgun. D.C. Code 7-2501.01(9).C specifically states the term firearm shall not include any device used exclusively for line throwing, signaling, or safety, and required or recommended by the Coast Guard or Interstate Commerce Commision.
I hope this information is responsive to your request. If you have any further questions please feel free to contact me at
Colin.Hall@dc.gov or call a member of the firearms registration unit at (202)-727-4275.
Colin Hall
Sergeant Gun Control Unit
Police Business Services Division
Corporate Support Bureau
Phone 202-727-9889