Ezekiel prophesied that those who are marked with an X (literally, a T-shaped, cross-shaped letter) will be spared destruction. John prophesied that those whose foreheads are imprinted with "the seal of the living God" will be spared (Rv 7:2ff). These prophecies help us appreciate the necessity and significance of Baptism and of renewing our Baptisms, for at Baptism we are sealed as belonging to God (see 2 Cor 1:22).
Every time we make the Sign of the Cross we can renew our Baptisms. For example, before hearing the Gospel reading at Mass, we make crosses on our foreheads, lips, and hearts. The cross on our foreheads marks our commitment to "acquire a fresh, spiritual way of thinking" by living our baptismal graces (Eph 4:23). The cross on our lips marks our commitment to "say only the good things men need to hear, things that will really help them" (Eph 4:29). In this way, we won't grieve the Holy Spirit with Whom at Baptism we "were sealed against the day of redemption" (Eph 4:30). By making the sign of the cross on our hearts, we commit ourselves to live fully our baptismal promises by loving the Lord with all our hearts (Mt 22:37; Dt 6:5).
You are marked, sealed, signed in Baptism. Live accordingly, and you will be delivered "from the wrath to come" (1 Thes 1:10).