The Christ inscriptions always bear the short form for " Jesus Christ" in Greek IC XC (IHCOUCXPICTOC=IESOUS CHRISTOS).
The halo on Jesus on the cross should always bear the inscriptions O, w and N (Greek = the being, the existing, he who is) to point out that Christ is God whose principal feature is beingness.

The Mother of God bears the short form, the initial and last letters, for "The Mother of God" in Greek MP OY (MHTHPOEOY = Mother to God).

In addition there may be inscriptions in other languages depending on where the icons originate; for example Armenian, Georgian, Syrian, Coptic, Arabic, Latin and Italian.