This is possibly a quellen-piece, but I'm not sure ... from one of those Q&A things in the Contra Costa Times:

Dear Joan:

Notice the crescent windows on outhouse doors. Do they have any relation or common history with the crescent on some Muslim country flags and the Red Crescent (counterpart to the Red Cross)?

Glenn H., Pleasanton

Dear Glenn:

The crescent moon symbol on the privy door is completely unrelated to the crescent moon we see on flags of other nations and organizations, which use the crescent as a symbol of unity.

The main reason anything was carved into the outhouse door was to provide ventilation and to permit light to enter while maintaining a certain level of privacy.

But it wasn't just a moon. Early outhouse makers also cut suns into the doors. And here's the surprise: The moons and suns were early versions of stick men and women designating men's and women's bathrooms.

The crescent, an ancient symbol for the Roman moon goddess Luna, was for the ladies. Sol, the Roman sun god, was for the gents. Over time, the men weren't so great at maintaining their potties, but the women took better care of their facilities. While the men's outhouses fell by the wayside, the women's became the standard and the moon became the universal -- and unisex -- symbol.