Acronyms:
MP= (Mhtep) Meter; greek for mother.
THY= Theou' (The greek letter Theta with the Y); "Of God" . Thus the inscription reads 'Mother of God' or "Theotokos" (God Bearer)
IC XC= Isous Xristos; greek for Jesus Christ.
The letters in the halo: O W N; greek acronym for, "He Who Is"