CCC 1235
Christian Mystery›SECTION TWO THE SEVEN SACRAMENTS OF THE CHURCH›CHAPTER ONE THE SACRAMENTS OF CHRISTIAN INITIATION›III. How is the Sacrament of Baptism Celebrated?
The sign of the cross, on the threshold of the celebration, marks with the imprint of Christ the one who is going to belong to him and signifies the grace of the redemption Christ won for us by his cross.