when i was younger there was a land owner that lived close to me had signs along his property that he painted on 4x8 plywood that said (no hunting fishing or trespassing, anyone caught on this land will be treated as a criminal and any shot heard will be a considered an act of aggression). he had no problems.
Having dealt with some issues similar in nature myself, its really hard to set cameras out thereafter. Deep sense of conflict as we want to do the recon, but don't trust our fellow neighborhood kids, neighbors, etc. I have not had any issues with my cameras disappearing ever since I attached a simple note to my cameras...If you find and take this camera, you better find the second one cuz I have your picture now!! Havent had another issue since!! Contact law enforcement and your DNR. Not only are these people stealing, but they are also trespassing. Both are against the law. Who knows if they were just hanging out in the cool spot, or casing your stuff. Good luck...