Recently I saw an sign at a barber shop on which I read on bold letters:
"Men's only"
Is this a correct writing?
I think that it has to be "Men only" to make clear that it is a barber shop for men only.
Or am I wrong and this spelling is correct and means something I don't know?
It is fine.
"Men only" would be ambiguous. Is it a barber shop that only provides its services to men? Or are women and children not allowed in the shop? What if a man comes in with his little daughter? Will the little girl not be allowed to enter the shop?
"Men's only" works fine because it means "Men's [haircut] only". So, yes, your wife and child can accompany you, but they can't get a haircut in that shop.
