IC XC NIKA

A nomen sacrum (sacred name), the convention in early Christian manuscripts where sacred names were contracted using their first and last letters, with a line (titlo) drawn over the top: IC = first and last letter of ΙΗΣΟΥΣ (I...S), Jesus. XC = first and last letter of ΧΡΙΣΤΟΣ (X...C), Christ. NIKA = Greek for "conquers" or "victorious." The "C" here isn't the Latin letter C — it's the Greek lunate sigma (Ϲ), which looks like a C and was common in Byzantine-era Greek. So ICXC is really IC ΧC in Greek letters, not Latin ones. ΙϹ ΧϹ ΝΙΚΑ "Jesus Christ Conquers" (or "Jesus Christ is Victorious").