I was wondering the same thing. Couldn't we put a sign right in front of the the bridge that just says "Mountain Bike Trails: Open/Closed" I know it would be a bit of a hassle to get out there and change the sign all of the time but it might help with some of these issues. I am in that area quite a bit and would be willing run down there and change the sign if someone asked me to do it, I think there is plenty of people that would be willing to do that.