Hmm, is this new? DTW is my home airport and I've never seen any such signs here. I'm pretty sure I would have noticed them with the many times I've been in the clubs.
I saw them about a year or so ago. I've visited the various DTW clubs a few times since and have not noticed them either. Perhaps the rules changed! I agree with the previous poster in that I chuckled at the sign while pouring my 3rd drink.