It doesn't matter how clearly they're marked. It doesn't matter if they're in the only place you could possibly put them. It doesn't matter if there is a visible line forming outside them. Customers will be unable to find the toilets on their own and will wave frantically at you for directions while you are attempting to serve someone else. If you make it to the end of the shift without having to redirect someone from the kitchen or storage cupboard then you consider it a major victory.