U+2CE9 Coptic Symbol Khi Ro

The Wikipedia has the following information about this codepoint:

The Chi Rho (☧, English pronunciation ; also known as chrismon) is one of the earliest forms of the Christogram, formed by superimposing the first two (capital) letters—chi and rho (ΧΡ)—of the Greek word ΧΡΙΣΤΟΣ (Christos) in such a way that the vertical stroke of the rho intersects the center of the chi.

The Chi-Rho symbol was used by the Roman Emperor Constantine I (r. 306–337 AD) as part of a military standard (vexillum). Constantine's standard was known as the Labarum. Early symbols similar to the Chi Rho were the Staurogram () and the IX monogram ().

In pre-Christian times, the Chi-Rho symbol was also used to mark a particularly valuable or relevant passage in the margin of a page, abbreviating chrēston (good). Some coins of Ptolemy III Euergetes (r. 246–222 BC) were marked with a Chi-Rho.

Although formed of Greek characters, the device (or its separate parts) is frequently found serving as an abbreviation in Latin text, with endings added appropriate to a Latin noun, thus XPo, signifying Christo, "to Christ", the dative form of Christus, or χρ̅icola, signifying Christicola, "Christian", in the Latin lyrics of Sumer is icumen in.