If a person has in openly in his possession a weapon that is obviously an NFA weapon, he is committing a crime, unless he satisfies the requirements for lawful possession of the NFA weapon.
I disagree. A person with an NFA weapon is not obviously breaking the law any more than a person driving a car on a public road is. Government authorization is needed for possessing an NFA weapon and driving on public roads.
Authorization for the NFA weapons is arguably much easier to obtain than a driver's license. No written test, no practical exam, and no physical required for obtaining an NFA weapon. A few forms, a fee, a background check and minimum age requirement are it.
ETA; I sent you a PM requesting a reply. Thanks for answering here.