I was open carrying at the time, and just put my stuff in my backpack "just in case."
I dont see any reason why this sign is legit, or would apply to a CHL or other license to carry, but due to the proximity to Lake Lavon, I figure i'd ask, in case it was some kind of weird edge case I dont know abut.
http://www.collincountytx.gov/parks/Pages/bratonia.aspx
http://www.rrcc.org/