Hear more and more of this. Used to be you could put up a stand etc and no one would even think of touching it. The NE Missouri Bowmen club does a 3d shoot monthly on public land. They get a permit from DNR to do it. Used to setup Fri night and take down on Monday. Now they have to setup Sat night and someone has to camp there, and take down Sun afternoon otherwise you guessed it, people steal the targets. So that cuts out the winter shoots we used to enjoy. Not enough daylight time.
I think I'd ask people, however, since there's the outside chance someone thought they were doing you a favor or even borrowed it. One 3d target got returned a year ago by a guy who borrowed it to practice. When we called his wife was home and she knew he had it and made him feel like **** for doing that and he brought it back. Jerk.
Sorry. As the Lord said "forgive them for they know not what they do" Some people are really clueless
Let it go and move on
sam