What is the fish symbol for Jesus? Greek ichthys

The fish symbol for Jesus is an early Christian symbol playing on the initials of the Greek word for fish, ichthys.

In Greek capitals this is written ἸΧΘΥΣ where the letters stand for

• Ἰησοῦς Χρῑστός Θεοῦ Υἱός Σωτήρ,
  Iēsoûs Khrīstós, Theoû Huiós, Sōtḗr
  Jesus Christ God’s Son Saviour

The single letters do not display the full grammar where God would naturally be read in the genitive, Theou, of God, not Theos, God. So the fish symbol certainly does not have any Trinitarian connotation that Jesus is God, and the symbol predates the development of the Trinity.