The Greek letters that make up the word for fish "icthus", also serve as an acronym, "Iesous Christos Theou Yios Soter’, which is translated as ‘Jesus Christ, Son of God, Savior’. We pronounce it "ick-thoos". 

The icthus fish symbol is used in some places as a secret symbol, because to openly declare yourself a follower of Jesus Christ could mean persecution or death. You might make a half circle in the sand with your foot and watch to see if the other person recognizes the symbol and completes the other half of the fish. 

The fish symbol is sometimes referred to in reference to Jesus calling the disciples to be fishers of men. They were to be intentional about sharing their faith and making disciples. A fisherman makes preparations; he chooses his bait and tackle carefully and then goes to the place where the fish are most likely to be. In the same way, we need to be intentional, "prepared to give any man a reason of the hope that is in us." One way we can be prepared is to strategically look for conversation pieces to get discussions going about spiritual things. For example, decorating your home or office with a Christian theme, or wearing Christian clothing and jewelry, or sharing inspirational gifts when appropriate.