In the US the greatest problem with law enforcement is ignorance. Now before you get excited about that statement, my reference is in the level of knowledge regarding the motor vehicle code as it applies to classic or historic motor vehicles.
The police academies here have little time to take a young man from being a civilian to a fully commissioned police officer. If you were to take a look at the laws he/she have to enforce, the volumes pile up higher than his head. Then take the court decisions that modify those laws, and then add the rules and special orders that are required knowledge. It is truly mind boggling. The end result is that the vast majority of the "street cops" have little knowledge of the special sections regarding your historic military vehicle.
For example many states allow an owner to register an appropriately old vehicle, usually 25 to 30 years since manufacture, using a "military registration number" such as might be painted on a bumper or hull. The title and registration will probably list that number, however the owner has the option of displaying the issued "collector car" or "historic vehicle" plate(s) OR using the painted number for identification. This means that no officially issued plate need be displayed, but one is probably required to be carried in the vehicle to be displayed upon request.
I know of one fellow with a well restored and equipped HUMV who regularly drives on and off a military post to pick up friends. The vehicle is NOT owned by the military, but because one HUMV looks like any other to the Department of Defense gate guards, he comes and goes at will. I suppose this is a dangerous tactic and the time could come where he and his HUMV might be parked in the impound lot.
The best defense is a good offense, it is said. So arm your classic historic military vehicle with all the documentation necessary to satisfy an police officers' curiosity. At the minimum you probably already have your registration and insurance papers. Add to this a copy of your state's motor vehicle law section covering your vehicle, especially if you have a "no plates" option. If all your required safety equipment (brake lights, turn signals, etc.) are present and working, then that's a good thing.
The worst thing a driver of a historic military vehicle can do if stopped by an officer "with an attitude" is to respond to his demeanor. You may well end up having to defend your position in court, and even worse, you might get your vehicle impounded.
Another issue that is really unclear in many areas is the level of driver's license required when operating "big rigs". In some states if the vehicle has air brakes, then a commercial drivers license (CDL) is required. Some states either limit or exclude historically licensed big trucks from carrying anything but passengers - no cargo even if it's your lumber for your garage expansion.
The bottom line is that you should know your vehicle and your laws, don't argue, and hope for the best! I have driven my Ferret over 6,000 miles in two states and have not been approached by an officer EXCEPT to take a look and enjoy seeing old military vehicles out on the road. My experiences in 38 years of law enforcement give me some background to comment on this, as my main tasks involved traffic enforcement and training police officers in accident investigation.