ΙΧΘΥΣ

The ichthys or ichthus (/ˈɪkθəs/), from the Greek ikhthýs ( 1st cent. AD Koine Greek [ikʰˈtʰys], "fish") is a symbol consisting of two intersecting arcs, the ends of the right side extending beyond the meeting point so as to resemble the profile of a fish. The symbol was adopted by early Christians as a secret symbol. It is now known colloquially as the "sign of the fish" or the "Jesus fish".

The first appearances of the ichthys symbol in Christian art and literature date to the 2nd century AD. The symbol's use among Christians had become popular by the late 2nd century, and its use spread widely in the 3rd and 4th centuries. The symbolism of the fish itself may have its origins in pre-Christian religious imagery. For example, Orpheus was described as a "fisher of men" as early as the 3rd or fourth century BC. The fish was used as a symbol in a number of other near-eastern religions as well, often as a sacred (or taboo) food. The fish was sacred to the goddess Atargatis, for example, who was said to cause tumors in those who ate them. Fish were only allowed to be eaten by priests during rituals devoted to Atargatis, in the belief that they represented her body. Despite the thematic similarities of these various sacred fish, some scholars have argued that there is no direct link between them and the Christian symbol or practice of the Eucharist; instead, the Christian usage was probably simply part of a larger, popular religious motif of the time. In the early Church, the Ichthys symbol held "the most sacred significance", and Christians used it to recognize churches and other believers through this symbol because they were persecuted by the Roman Empire. The Ichtus symbol is also a reference to "the Holy Eucharist, with which the miracle of the multiplication of the loaves and fishes had such intimate connection both in point of time and significance." While many Christians hang a cross necklace or rosary inside their vehicles, "the fish sticker on the car is a more conscious symbol of a witnessing Christian—significantly, unlike the former, it is on the outside of the car for everyone to see".

...
Wikipedia