These signs are italic forms of the first
letter, alpha, in the
Greek alphabet. It is used in dozens of technical and scientific
systems. British lawyers often mark their folders with this sign to
indicate that the case is closed.
In Christian symbolism is a stylized fish, a symbol for Jesus. The word fish in Greek is a combination of the initial letters of the name Jesus Christ, Son of God, Saviour.
For further data see , another Jesus symbol, in Group 26.