The X in X-mas comes from an initialism of the Greek name for Christ ΧΡΙΣΤΟΣ, a shorthand employed by Biblical scholars and others to abbreviate things to do with
Jesus or the Cross (writ both large and small—Celtic monks in Germany
monasteries incidentally invented a lower-case script with punctuation
for the Greeks to make reading easier) and these signs and signals are
reflected in the iconography of Jesus and the saints in hand-gestures that amount to a sort of finger-spelling. These poses, each understood to audiences in a specific way, were in turn a traditional and long-established system of rhetorical gestures used by speech-makers in Antiquity to cue their listeners to something important or to mark a transition.