My first interaction with the law was the s/n verification. My M38A1 started life in the Army at Fort Riley, was x-ferred to the Kansas Guard, then surplused out of Riley to a local volunteer fire department, where it spent many well-maintained years as a field-fire truck. That department eventually sold it at auction to a guy in KC, who titled it in Missouri even though he lived in Kansas. He used it as a parade vehicle. I bought hit when he and his wife had a living estate sale, as they were downsizing to a retirement community.
This process entailed me having to trailer the jeep once to the local office, where they couldn't handle it, then to the "special" office 50 miles away - where they tried, but told me I would have to wait for Trooper Tate. Who's father was ill. So, the next week, I trailered it down there again - and I'll give Trooper Tate this - he spent an hour in the July sun trying to find a number on the vehicle that would work - but couldn't. It had long since lost it's data plates, and the s/n plate had a stamped number on it. Not good enough for the KSHP, so I had to spend $700 to quiet the title, and get a state VIN.
I get through all of that mumbo-jumbo, get my court order, and call Trooper Tate to schedule the work. He remembers me and tells me he'll come to me and do it there. Nice guy. Flash forward - I get new data plates made, including the patent plate. I pull off the plate that had the hand-stamped number on it. On a whim, I turn it over... and there, hard to read but readable, is the original s/n. One of the previous owners, probably the Guard or VFD, had simply turned the plate over and stamped it. There's $700 I'll never see again.
I've got it registered as a historic vehicle, which means in Kansas I'm not supposed to use it for regular driving - but I can motor around "for pleasure." I'm also allowed to take the plate off for parades and shows (have to keep it with me) which I think is a fair compromise.
I did have fun driving on to Fort Leavenworth - with the dummy machinegun mounted. The rent-a-cop at the gate wanted to see the registration on the gun - I told him it wasn't registered on post - because it wasn't a gun. Which caused him some consternation. I invited him to clamber up and pop the feed tray cover and check for himself. He did, and wanted to assert it was too a gun because it was cockable. Heh. It has a block of steel with a weak spring on it - and the belt is held in with welded-in pins. I can't wait to go through there with the M20 75mm Recoiless mounted for the next militaria show...
I've been stopped once. By a cop who wanted to argue with me that my bumper markings were incorrect. I asked him if he really felt he was fully conversant with 1950s/early '60s bumper markings? And then showed him the picture of the prototype vehicle.
Other than that, they like to come over at parades and marvel at the reckless rifle.