While digging I learned that this is a lobed Byzantine cross with a rather early form of the 3 lobes on each arm, representing the 12 (3 x 4) apostles and it is on a crescent moon, probably representing the Mother of God and her womb, the holy cup (or grail).
The inscription uses iconographic style abbrevions (first and last letter) with a dash over them. It says
Fos Christis fotise panta
Light of Christ has lit all/everyone