The most important sexual organ is, we are told, the brain. When it happens to you, you don't abstract the experience through high-flown theoretical language. A symbol is an arbitrary sign, somehting that is simply chosen to stand in for something else. According to C. S. Pierce, another type of sign is an icon, or a representation that attempts to simulate visually the appearance of the thing that it represents, which is what happens in a drawing or a painting. Preserved in the index is the remnant of an unmediated contact with real, independent objects and beings in the world.
Photographs are indices.
So are bruises. Abstract patterns, Like veins running through marble. Once I saw a show of Italian terra cottas at the National Gallery. Near the end of the exhibit was an unspeakably beautiful, life-size image of the dead Christ. The museum guard shouted something and I quickly retreated, acknowledging my transgression but secretly happy that I'd gone through with it.