According to CPW regulations brochure, it is unlawful to "Post, sign or indicate that public lands, not under an exclusive-control lease, are private." These folks might think they are getting around posting it as private by saying that it is closed by a government agency. It seems to me to be forging of a government document at this point.
I frequent a clear cut on public in a spot that holds bear, deer, moose, and elk. Tons of sign in this place all the time. There's been a semi-permanent stand there for a long time. Someone last year started to post "private property" signs on printer paper at the main entrance. There are about 5 layers of staples and paper edges because it keeps getting ripped down. Guess it kind of worked, one buddy got cold feet about going in there...
I saw something similar this year with State Trust Land. Someone had posted "No Trespassing" signs in one particular area of the STL's that butt up against some private, but those lands are all one contiguous piece of land. There weren't any signs or closures on any other parts of those STL's, and the DOW's STL brochure shows them still as valid hunting areas. You've got to know your stuff out there because there are some that will take advantage of those that don't know what's going on. Also, this year the wardens were busy kicking folks out of those same lands that had set up camp in there. There is no overnight camping on those lands.
I would send those pics along with the location to the local CPW warden and ask them about it. They would probably be pretty interested in finding the person posting those.