Tecnically, they are only poaching if they do not have the proper license(s) or permit(s) or are attempting to take game out of season or after legal hours... However, they are trespassing, and that stand is mine. I would also attempt to backtrack them to their point of entry and set up a trailcam to get a pic of them, their vehicle and/or plates, and a nice note would be left at their stand site explaining it's not nice to trespass. The law would be paying them a visit if I was successful in figuring out who they are.

This of course assumes I had properly posted the land, which I would have.