When you see toilet signs, they look more or less like this:
It is clear who can enter either of them.
Now, say you are designing the signs for showers and you want to distinguish between the ones for men and the ones for women. How would you do it?
Considering the women (and the men) have showers without clothes, the dress-shape-for-women is not valid. What can be painted to clearly indicate the difference without any kind of text?
I found this one but it is still a bit creepy: