One of the better ones I have seen was on a ranch out west of Leaky, TX
They were totally homemade, one foot wide white painted boards with stenciled in red were these crude drawings of a hog-rhinoserous eating a guy.
They were crazy looking. Oh, and there were about every hundred feet for about half a mile.
Kind of a just keeping You safe kind of deal mixed with a slight silence of the lambs subtle hint kind of thing.
I would not put any sign up and just be vigilant about what goes on around and in my property. Trying to warn folks about your intentions wor doing something out of the ordinary will just get you unwanted attention. My buddy built a palisade on the front of his ranch house, looks really cool and cuts down on the road noise coming from the FM road that goes by there. Yep, you guessed it, local cops just new he was a doper and up to something. So they tried to sting him with some kind of crap set up. They failed miserably.
"We did not think anything until you put that crazy fence up, we just know you are dirty!"