I don't think there has been an outcome yet on
this but it is in a similar avenue.
Boyd's gaming group specifically posts no firearms signs at their properties. Locally(I live in Las Vegas) this kind of issue would be complicated by the fact that those signs have no force of law. They can only tell you to leave if they discover you have a firearm, not legally compel you to be disarmed with a sign.
In general, I think the businesses are removed from liability, but as we can see there was at least one lawyer willing to take on a case of this nature.