I get permission to hunt various pieces of private property, sometimes I am the only hunter allowed, sometime 1 or 2 other hunters and I try to get to know the other people who have permission, so vehicles, blinds, stands are all known of who owns what. If I see a unknown stand on shared property I call the folks with permission to see who it belongs too if none of them I call the landowner. If the landowner doesn't know then its fair game to take the stand/blind and move it to another piece of land I hunt on for me to use.
I can't stand tresspassers, especially since much of the private land I hunt I do labor for the landowner or I bring them gifts, such a Christmas Ham, gourmet coffee, booze, etc.