In KY, signs DO NOT carry the weight of the Law. If there's a sign at a place that serves alcohol, then it's a SUGGESTED No Fly Zone, due to KY laws around bars.
The signs at the Louisville Zoo used to have the force of law due to Jefferson County's ordinances, but KY has a preemption law now.
They may still have the signs up quoting the outdated Jefferson County ordinance that banned carrying at the zoo, but if its still up it would be illegal to enforce.