The symbolism of using the moon and stars on outhouses is believed to have originated from pagan religions and was used instead of words because of the high rates of illiteracy in earlier times.
In frontier days the moon stood out as a feminine symbol, so public outhouses were affixed with crescent-moon cutouts to signify that the outhouses was intended for use by women.
Conversely, the sun, star or sunburst pattern was used to signify the male outhouse, as the sun stood for masculinity.
In addition to recognizing the intended users of the outhouse, the shaped cutouts also provided ventilation. The cutouts keep the structure cooler in summer months and provide a little bit of fresh air for the outhouse occupants.
The moon and star shapes on outhouse doors also provided access to light while visiting the facility. Since a lantern could not be taken into the outhouse, the cutout allowed light from the moon and stars to enter into the outhouse at night.