While I was looking at all that stuff about the vesica piscis, I suddenly realized that I had seen that same shape used someplace else in an entirely different context. Venn diagrams! It’s totally the same. Check out the Venn diagram on the left and the vesica piscis on the right.

Also, according to one definition I just found online of the vesica piscis (also called the mandorla), there is even a similarity in meaning:

The Mandorla, a symbol that is all but unknown today. It was used during the times of medieval Christianity. It is an ancient symbol of two circles coming together, overlapping one another to form an almond shape in the middle. Jensen describes the Mandorla as similar to the image of two Mandalas (Sanskrit word for circle) merging together until an almond shape is formed in the center. Also known as the “Vesica Piscis”, symbolizing the interactions and interdependence of opposing worlds and forces. The circles may be taken to represent spirit and matter or heaven and earth.

Crazy how things “come together” like this. I always really liked Venn diagrams, because they are very accurate representations of a particular kind of relationship.