The Ichthus is a fish symbol Christians, often through bumper stickers, display on their cars as a sign they are a believer. The symbol is often found in jewelry offered through Christian stores.
The name itself is sometimes utilized to denote certain activities, such as the annual Ichthus Music Festival held in America (the oldest Christian music festival in the U.S.). Few, however, consider how the symbol was linked to belief in Jesus Christ.
Though its origin is somewhat uncertain, some believe the association of fish and Christianity began with the Greek word ichthus (or ichthys). This word is translated twenty times in the New Testament as 'fish.' This association was likely encouraged by the fact that at least half of Jesus' original twelve disciples were fishermen.
It was Christ Himself who told Peter and Andrew that instead of catching ichthus He would train them to catch men (an allusion to preaching of the gospel.
And He said to them, "Follow Me, and I will make you fishers of men." (Matthew 4:19, see also 13:47 - 48, Mark 1:17).
According to several Bible commentaries, some in the early New Testament church used the Ichthus symbol as a secret reference (cipher) for Jesus. This correlation apparently led to the creation of an easy-to-draw shape as a profession of faith. Roman Catholics believe Clement of Alexandria made the first written correlation between Christianity and the fish-like symbol (1913 Catholic Encyclopedia).
Religious correlation
The religious correlation between the Ichthus symbol and faith, albeit pagan, pre-dates the birth of Jesus. The pagan fish deity Dagon was one of the gods of Assyria and Babylon. The Amorites (some of which lived east of the Dead Sea) and the Philistines (Judges 16:23, 1Samuel 5) also worshipped Dagon, who represented fertility. Anciently, he appeared either as a half-man half-fish or as a man wearing a fish-shaped head.
Some have thought the 'star' which led the Magi to worship Jesus was a bright object in the shape of a fish (Ichthus). After the New Testament church started on Pentecost in 30 A.D. it did not take long for violence to visit those who dared to live "the Way" (Acts 9:2). The first Christian martyr, Stephen, died just two years after Jesus' resurrection.
According to some non-Biblical traditions, early believers used the Ichthus to mark off meeting places, designate the tombs of Christians, and to generally identify each other.
One tradition states that when a Christian approached someone on the road he or she would draw a half-arc on the ground. If the other person also drew a half-arc, completing the picture of the Ichthus symbol, then both knew the other person was a believer. If true, such an exchange could have helped Christians avoid some potential persecution.
For whatever reason, the Ichthus or 'Jesus Fish' fell out of popular use for many years until the early 1970s. It experienced a resurgence beginning around 1973 and has since become a worldwide icon of the Christian faith.