Love that sign. The poison ivy is the credible deterrent.
I react to Poison Ivy, but manageably. Mrs. BD reacts with hives if she gets near it. (Poison Oak is a southeastern US thing and I don't think I have seen it.)
Cape Cod is full of Poison Ivy the second you get off a trail. We found a solution for her. After a hike, wash her legs with Dawn or some other dish detergent. Then use this magic stuff.
It saves a trip to the ER to get steroids.