Tom,

Are you aware that the Postal Inspectors of the US Postal Service are armed ? Check out their site:

http://www.usps.com/postalinspectors/

This is from their FAQ:

3. What authority do Postal Inspectors have under the law?
As sworn federal law enforcement agents, Postal Inspectors have the power to serve warrants and subpoenas issued under the authority of the United States; make arrests without warrant for postal-related offenses committed in their presence; make arrests without warrants for postal-related felonies cognizable under the laws of the United States, if they have reasonable grounds to believe that the person arrested has committed or is committing such a felony; carry firearms, and make seizures of property as provided by law.

Dave