I was thinking out loud of what I'd do.
Back in my offroad motorcycle days I'd use clear box tape to attach a copy of the title to the underside of motorcycle seats for proof of ownership. On one particular outing, a police cruiser followed me down a creek side trail and the officer said he stopped me because of reports of stolen motorcycles nearby. I unbolted the seat and showed him a copy of the title, which satisfied him enough he let me be. Yep, I had my drivers license on me, too.
So, I was thinking a little piece of paper for a firearm that someone in authority may question may work in a similar fashion.
So what piece of paper are you planning on carrying?
There's no title, there's no registration...at least in most states. A receiver when purchased isn't classified as a pistol or rifle, but as "Other firearm".
Inquiring minds want to know.