I work in a federal building. It is posted as no weapons
of any sort. The proper cite isn't the U.S. Code, but the Code of Federal Regulations, specifically, Title 41 CFR § 102-74.440:
What is the policy concerning weapons on Federal property?
Federal law prohibits the possession of firearms or other dangerous weapons in Federal facilities and Federal court facilities by all persons not specifically authorized by 18 U.S.C. 930. Violators will be subject to fine and/or imprisonment for periods up to five (5) years.
Now, it's clear that, in a bit of circular reasoning, the regulation cites the same vague provision of the U.S. code as its statutory authority.
But I know from bitter experience, one is ill-advised to carry a weapon of any sort into a federal building. As I am a federal employee, they chose the equivalent of "non-judicial punishment," but punishment it was. (If you're wondering, the weapons at issue were not firearms. So, I kept my job. Barely.)
If you want to be a test case, hire Alan Gura or Robert Michel and have at it. But you'd best be an ideal candidate, with your ducks bill-to-butt before testing both the statute and the regulation.