The Cross represents the symbol of Christ's death; the ensign and chosen symbol of Christianity and of a Christian people. The sign or mark of the cross is made during Catholic devotions.
The Cross as a Christian Emblem
After the conversion, so-called, of Constantine the Great (B.C. 313), the cross first came into use as an emblem of Christianity. He pretended at a critical moment that he saw a flaming cross in the heavens bearing the inscription, "In hoc signo vinces", i.e., By this sign thou shalt conquer, and that on the following night Christ himself appeared and ordered him to take for his standard the sign of this cross. In this form a new standard, called the Labarum, was accordingly made, and borne by the Roman armies. It remained the standard of the Roman army till the downfall of the Western empire. It bore the embroidered monogram of Christ, i.e., the first two Greek letters of his name, X and P (chi and rho), with the Alpha and Omega.
The Easton Bible Dictionary provides the following definition, meaning and emblem for the Cross Christian Symbol in the Bible. In the New Testament the cross was the instrument of crucifixion, and hence used for the crucifixion of Christ itself (Eph. 2:16; Heb. 12:2; 1 Cor. 1:17, 18; Gal. 5:11; 6:12, 14; Phil. 3:18). The word is also used to denote any severe affliction or trial (Matt. 10:38; 16:24; Mark 8:34; 10:21).