The earliest uses of the Ichthys (Greek for "fish") symbol date back to the 2nd and 3rd centuries CE, where it appeared in graffiti, inscriptions, and funerary epitaphs. Rather than a secret code ...

The Greek word for fish is "ichthys." As early as the first century, Christians made an acrostic from this word: Iesous Christos Theou Yios Soter, i.e. Jesus Christ, Son of God, Savior.