“The Chi Rho is one of the earliest forms of christogram [that is a monogram for Jesus], and is used by some Christians. It is formed by superimposing the first two (capital) letters chi and rho (ΧΡ) of the Greek word “ΧΡΙΣΤΟΣ” [that is, Christ] in such a way to produce the monogram. Although not technically a Christian cross, the Chi-Rho invokes the crucifixion of Jesus, as well as symbolizing his status as the Christ.” (WP:CC-BY-SA)
Because crucifixion was considered a shameful way to die (Paul spends a lot of time working this out) and the cross a painful reminder of the tyranny and domination of the Roman Empire, the cross was not immediately adopted as a symbol of Christ and Christianity. For this reason, the Chi Rho actually predates the cross as a symbol for Jesus Christ.
The Chi Rho on the front of this week’s bulletin is a stylized variation (that could also be interpreted as a monogram of the cross) by Placid Stuckenschneider. A more traditional version can be seen above.