I used to carry a copy of the trespassing law in my wallet from my Jeepin'/fishin' days and it says they have to tell you that you are trespassing before you are trespassing, either verbally or by posting it. As long as they leave the gates wide open and there is nosign, I'm good to go, at least until they see me and chew me out. It's the same in most states, but some also consider a locked gate and fence as a warning, but I wouldn't climb over a locked up fence anyway.