Blue/White Thruway Question Mark Signs?!?

OK, I feel stupid asking this, but my family is so annoyed. We live in Upstate NY, and when we travel on the thruway- like I-90- I always spot these blue signs with a white question mark on them. The thing is, even though they look professionally done, they are almost always on the BACK of a real sign and/or upside down, so I don't think they're legitimate, I think they're a joke. Sometimes I also see them just stuck into the ground at the top of a pole by the side of the highway. What are these?!?