Hunting unfenced, unposted, private property?

If your hunting and end up on private property that isn't fenced or posted are you trespassing? Is it something we should even concern ourselves with? Sometimes unfenced and unposted is obviously private land and other times it's not obvious.

This season I was exploring a bunch of really old logging roads on the atv and came up on a gate. When I went past the gate I looked back and saw a private property sign!! Apparently somewhere along the way I had entered private land!! Funny thing was, there was no fencing, no fields, and no obvious signs of recent human movement. I admit that after seeing the sign I turned around and proceeded back the way I came regardless of what the sign said ! This was an expensive commercial gate, not your average cow field gate so I think it was legit.

As ethical hunters how far should we go out of our way to ensure we are on crown land??? And not unposted, unfenced private property?