A vesicle pisces is the name that author Philip K. Dick gave to a symbol he saw (on February 2, 1974) on the necklace of a delivery woman. The symbol was used by the early Christians.
The symbol resembles a fish, in profile. However it is not a picture of a fish. It was a symbol consisting of two intersecting arcs. Scott Barbacki speculates that P.K.D. may have interpreted these arcs as a portion of DNA's double helix.