It has been my understanding that only an officer of the BATFE can require you to show your original form 1 or 4. I carry photocopies of all my forms in my range bag along with ones in every vehicle on and off road that I own and obviously in my home. I also have scanned pdfs of my forms on my phone. You have to remember possessing a suppressor or sbr or other NFA items in and of itself is not a crime. A LEO would have to have a reasonable suspicion that you are possessing the item illegally to detain and question you about it. If I were stopped and questioned, I would politely ask them if they were aware of the fact that only an ATF agent can require you to produce the paperwork, but out of courtesy (and not to escalate the situation) I will show you a copy of the form. If that doesn't satisfy them, then tell them I will meet them at their office with the original stamped form along with my lawyer the next day and they might want to have an ATF agent present as well.