The door to a historic mosque in Shiraz, Iran, has two knockers, one for women (on the left), and the other for men (on the right). The knockers make a different sound when knocked, alerting whoever is inside the gender of the person at the door.

The knockers have different designs. For women the design is one of flowing curves. For men the design is a relatively simple shaft. The analogy to the sexual organs of women and men is clear.

In this case of this photo, the two men in their 40s who explained the design to me giggled like teenagers as they explained the difference. Personally I think it is wonderful that a sense of humor can be maintained in the design of a holy site.