Chi-Rho ☧ originally a Symbol of the Centurion

May 2011
Rural Australia
I see. Probably because archaeological finds do not show the sigils.

The sigils are collected (as outlined in the OP) in ...... Michael Avi-Yonah, Abbreviations in Greek Inscriptions, Quarterly of the Department of Antiquities in Palestine (Jerusalem: Government of Palestine, 1940) As reprinted in Abbreviations in Greek Inscriptions Al. N. Oikonomides, Professor of Classics Loyola University Chicargo. Illinois,ARES Publishing 1974., p.112, also see a variation of the Chi-Rho in the Meggido inscription - “the Chapel of the Centurion”).

An extract of the relevant entries is shown at post #6.