Christian Fish.

Large numbers of cars have some sort of bumper sticker variation of the "Christian Fish", or the Ichthys. But what does the Ichthys mean?
Ichthys comes from the Greek word for fish. ΙΧΘΥΣ (Ichthys) is an acronym for Iēsous Christos, Theou Yios, Sōtēr -- which means "Jesus Christ, God's Son; Savior".
Historians believe the fish shape is an adaptation based on an Early Christian symbol resembling a cross for the eye. Other historians believe the fish symbol in Christianity came from a strong Roman influence in which fish were often incorporated in depictions of Roman gods.
Ironically, the shape didn't become popular in recent history until the early 1970s, when the Vietnam War caused reason for rebellion among younger generations. Since its use during the peaceful rebellions of the 70s, the Ichthys can be seen nearly everywhere... though most commonly stamped on the bumpers of cars.
The fish represents many themes and motifs in the Bible -- most notably the 12 Apostles (many of whom were fishermen). Perhaps the most famous "fish" story told in the Bible tells of a boy bringing baskets of five small loaves of bread and two fish. According to the story, this shortage of food was meant to feed five thousand. Jesus multiplied the food, and fed all the people. However, my favorite interpretation has been told time and again: Jesus and his disciples are known as "fishers of men" -- rescuing even the most downtrodden souls and giving them new life through the discovery of God.