Can't say they monitor detecting posts, but sure they monitor e-bay finds being sold.
Ok, I do for a fact know the Bureau of Tobacco and Firearms monitor newspapers. My one buddy, back in the late 80's was a curator for a museum in South Jersey and his museum was displaying relics from the P-47 aircraft squadron that was stationed in Millville NJ during WW2.
Well, since the airbase was a training base for the fighter pilots, there were quite a few crashes, with fatalities. He spent endless hours researching and many trips to the Smithsonian getting copies of the accident reports and then he would excavate the crash sites for whatever was left to salvage and then put on display in the museum at the airport.
One of his goals was to recover the 50 cal machine gun from one of the crash sites. Of course that was always one of the pieces the US Army Air Corp always tried to recover, but usually leaving many other parts behind.
It just so happens one of the crashes was in a local lake, and although parts of the plane were recovered, not the part that had the guns. In the late 80's this lake was drained for the first time since it was built in the 1860's, yes, lots of metal detecting finds.
My buddy was so anxious to find that plane, he took a pram and waded out into the lake where he thought the partial plane still layed in about 3 feet of remaining water and yes, he found it.
He did recover a bent gun and many clips of live 50 cal ammo. The Atlantic City Press had a front page photo of him with a big smile on his face standing in the water holding the belts of 50 cal bullets.
The next day he had the Federal Agents knocking on his front door, confiscating the gun and ammo, which they said was illegal to have.
So, yes, without a doubt there are people watching and looking but I am not so sure about on metal detecting forums, that would be conjecture until someone states a factual happening.....
Don in SJ