A phylactery was to be worn on the forehead of a Hebrew man (Exod. 13: 9, 16; Deut. 6: 8), and in Ezekiel's vision of the future (9: 4) the righteous are to be branded on the forehead with the letter Taw (a cross, X, in the old Canaanite Script). So also in Rev. 7: 3 the seal of God is set on the forehead of his servants. The early Church adopted the taw as an appropriate symbol of the cross of Jesus, and so a specifically Christian symbol.