IHS AND CHI-RHO
The letters IHS often appear on liturgical items, building plaques and gravestones and sacred vessels. IHS is a shortened form of the Greek word for Jesus.
The letters X and P are often used as another symbol for "Christ". The first two letters of Christ's name in Greek are X and P. In the Greek alphabet X equals CH and P equals R.
Also known as the CHi-RHO cross, the letters are usually inscribed one over the other sometimes enclosed within a circle becoming both a cosmic and a solar symbol.
Anchor, fish, and Chi-Rho symbols from the Catacombs of St. Sebastian.