Some jurisdictions apply the law that way, but if you read it, what the local LEO sign off is supposed to do is pretty much the same as the current "instant check" does. That is to certify that you are not a criminal. There are proposals to either remove the discretion of the local LEOs, many of whom won't sign the form for anyone for any reason, except sometimes for friends who contribute to their reelection funds, or alternatively to replace it with a call to the "Instant Check" folks.
At the federal level, you do not need to justify why you want that cannon, or machine gun. At the federal level you submit the signature card, pay the tax, and after a ridiculous delay, get your stamp and can have the cannon or machine gun transferred to you.