What it is
Ichthys (ΙΧΘΥΣ) is the Greek word for "fish." For early Christians it carried a second life as an acrostic: the five letters stood for Iēsous Christos, Theou Hyios, Sōtēr — "Jesus Christ, Son of God, Savior." A name, a creed, and a memorable image packed into a single five-letter word.
Where it comes from
The fish is one of the earliest Christian symbols. It appears on gravestones, on the walls of catacombs, and on household objects from the second and third centuries — the period when Christianity was still an unauthorized religion in the Roman Empire. The acrostic reading of the word is attested in early Christian writers; the simple two-arc fish outline appears even earlier as a visual device. The familiar story that early Christians used the fish as a discreet recognition sign between believers is widely repeated in modern retellings; the historical evidence for that specific practice is mixed, and the more confident statement is simply that the fish was among the earliest and most common Christian emblems.
The form
The simple outline — two intersecting arcs forming the silhouette of a fish — is among the simplest religious emblems in the Christian visual tradition. Drawn with a single continuous gesture, it can be scratched into stone, traced in sand, or stamped on the seal of a letter.
Where you'll see it today
The ichthys is widely recognized in modern American Christianity. It appears on bookstore signage, on the back of cars, on t-shirts and jewelry, and as a decorative motif on Bible covers. It carries less liturgical weight than the chi-rho or the cross but more personal, affectionate weight — a quiet sign of identification more than a formal emblem.
Why it's the SumBible footer symbol
The footer wants a quiet, ancient mark of Christian identity — not a formal emblem but a humble one, fitting for the part of the page that sits below the substance. The ichthys is the right shape for that register.