Reminds me of those signs on the interstate pass throughs that connect one side to the other, that cops often sit on. The sign says something like "authorized vehicles only" because presumably every one needing to turn around would use them to u-turn on the interstate, which is likely considered to not be safe. I used one to turn around one time and when called out by my kid, I assured him that I was authorized. I have no idea who is actually authorized to use those, outside of emergency vehicles.