Once upon a time I had a pre-WWI sheet of ordnance pieces gifted from a central repository to different locations (the Memorial Hall at Philadelphia's Belmont Plateau being one) that detailed what they were and where Uncle Sam acquired them (in this particular case, two Spanish 18 lb long guns from Cuba, IIRC). IIRC I sourced that from the National Achieves down in DC.
I believe that the Center for Military History now holds sway over all those memorial pieces, or at least thinks they do. In one particular case I'm familiar with, one of those stone post-WWI American Legion Halls had a German WW2 7.5cm AT gun out front. The Hall had been sold off ages ago and went through a couple of owner turnovers before winding up with some artistes, who painted the aforementioned gun a hot pink.
One of them told me that a USAF flatbed with a small crane showed up one morning. He walked out with his coffee and said, Bugs Bunny style, "whatchya up to, Doc?"
Long story short, dude got his lawyer on speed dial 'cause it falls under the laws of the Commonwealth ("yeah, we've been de factor owners of it since the folks you relinquished it to have been out of the picture for +25 years")
The flip side of the coin is how fast the government snapped up a German 10.5cm after another defunct AL Hall was purchased by folks who turned it into upscale condos - the difference there being that it was only the first turnover.
Make sense?