They need to be told in person or written to stay out. If one of them gets hurt or kill on your place the family could sue you. I have seen it in Texas where some boys climbed over a fence right by a posted sign. They were swimming in a pond and one drowned. The family sue the land owner.Liability for something I have no control over is one of my greatest concerns. I posted a couple years ago about some kids trespassing and riding 4 wheelers on my place up there. The first time they ignored a two “keep out/no trespassing“ signs and left the gate open, so I put a lock on it. The second time they bypassed my lock and chain but attempted to close the gate hoping I wouldn’t notice, so that told me they knew they were doing something wrong. I finally had to chain it so that they’re going to need bolt cutters to get in.
To be honest, I wouldn’t really care about them riding around when it’s not hunting season, but I don’t trust people not to do stupid sh*t and then try to blame someone else for their dumbassery.