In any interaction, the stronger party has an obligation to the weaker.
In any interaction, you (or at least, I) are always the stronger party.
Fences over Signs
Prevention over Punishment
'No Trespassing' signs are meaningless without accompanying fences.
But in the presence of a good fence, the 'No Trespassing' sign itself is quite meaningless.
Thus, leading one to believe, it is the fence that ultimately matters, not the sign.