It's private property, the fact that you enter 'wrong side' is irrelevant so long as the owner has signed this correctly and adequately, it's not his problem as the law does not prohibit such set ups and occasionally traffic drives on the right in nominally left side driving countries.
I'd imagine if there are signs up saying "exit only" or "no entry" then the driver attempting to enter this way would be liable and their ins. company would settle with or without their consent (subrogation).