At the Angelus on Sept. 11, Pope Benedict talked about how the Mass is linked to the sacrifice of the cross. "The Cross is the moving manifestation of the act of infinite love with which the Son of God saved humankind and the world from sin and death. For this reason, the sign of the Cross is the fundamental act of our prayer, of Christian prayer. Making the sign of the Cross...means saying a visible and public 'yes' to the One who died and rose for us."
I have to admit that sometimes I just make the sign of the cross in a hurried way, without really reflecting on it. Yet the pope calls it the fundamental act of Christian prayer. That's a good reminder for me!