Other than NFA firearms (machine guns and sawed off shotguns etc) there are no
federal laws that I know of that would apply. If you have a BATF form 4 with
stamp affixed you can even have a machine gun. I assume the CG just wants to
"secure" the weapons during their illegal search so they know where they are.
State and local laws will run the gamut from "you can't have one" to no rule at
all.
Md is not one of the more gun friendly states. You better ask the state and
locals ... and get the answer in writing.

http://www.packing.org/

might give you some insight.