I'm pretty sure it's not "unmarked". The lighting conditions are awful, and faded black paint on the upper 1/4 surfaces of OD green paint simply makes it really hard to see distinguishing markings. It'll always say United States Army anyways, as outside of a few notable operators, the US gubmint are the only ones that operate them over US soil and the Army (which includes the National Guard and Reserves) only fly them in that color scheme.

It MIGHT be possible with some camera trickery to figure out the tail number on the tail pylon, but you're not really gonna get anywhere with it. The crew and their command already either knows about it, and they got peepee spanked for it, or they were told to do it anyway.

This is an A+ model (not likely cause most have been retired) or an L model (almost 100%) due to a few distinguishing features I can go into if the geeks really want to hear it. Point being, It's almost certainly an NC Guard bird.