I agree with the poster that said this should be a no-brainer. It's not yours, don't use it. For those that feel it's ok to use the stand since it is on PL and against the law (assuming it IS against the law), how far a stretch is it from using it to taking it home with you? After all, it shouldn't have been there, right?
Now, if I knew it had been left there for days/weeks without use, my thinking may change. Or, if the stand was left on PL that was a high pressure area with limited acreage.
But my initial assumption would be the guy likely spent time scouting the area and put it up the day/night before.