This image was sent to us by Sean Wright, a long-time Roman Catholic contributor to this site. He explains:
"This cross betokens the Sacrament of Confession (a.k.a. Penance or Reconciliation). A priest's stole is folded here to form a Greek Cross. The handles of the keys incorporate an IHS and Chi-Rho, both symbols of Jesus, and are the sign of binding or loosing from sin. The crown and cross forming what may be called "pommels" on the handles are a sign of the "royal priesthood" shared by all those baptised in the name of the Trinity.
Ordinarily, when the keys are displayed, the handles are placed on the bottom and the blades are aimed at heaven to show from whence the source of the spiritual power of binding and loosing is derived.
The stole itself, of course, symbolizes the legitimate authority of a priest or bishop to grant sacramental forgiveness and absolution in the name of Jesus. That the stole is shaped into a cross is a sign of the sacrificial Crucifixion of Jesus by which salvation is won, the Crucifixion being the event which won this great power to reconcile sinful humanity to the all gracious God.
The keys are facing down here (if indeed a key can face in any direction) to demonstrate the spiritual power being put to use, possibly also denoting that the power is being employed by someone other than the pope."
1 Pet. 2:9