tmorone, what state do you live in? As Willie Lowman correctly pointed out in this thread
, the Form 4 is an affirmative defense against charges of owning an unregistered NFA firearm.
In plain English, that means you are assumed to be breaking the law until you prove you meet an exemption. The Form 4 is that proof.
Now, is the RO law enforcement? Probably not, but we live in a world of liability and potential liability, and one of his responsibilities is making sure no illegal activity is taking place on his watch.