Constantine 1×07: Blessed are the Damned.

John summoning an angel/summoning Manny.

“By the divine power that holds the balance, bring forth your servant of ministering. By your wisdom and your justice, your will be done. Please?”

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Update #1 from Catholic.com:

You are speaking of the chi-rho monogram. Though the two letters look like P and X in the English alphabet, they are actually chi (looks like X) and rho (looks like P) from the Greek alphabet. They also happen to be the first two letters of “Christ” in Greek (Christos). Hence the chi-rho monogram is used as a symbol of Christ, Christianity, and Christians.

Update #2 from Wikipedia:

Update #3 from Wikipedia:

I missed out on the Alpha (left) and Omega (right) symbols that Constantine had drawn into the sand.