In many churches, when people are baptized, the sign of the cross is also traced on their foreheads. This simple act is steeped in biblical stories about being sealed on the forehead, is an ancient practice within the church, and has a profound theological meaning.
Here is the short version of this long and rich history.
Cain, Passover, Ezekiel, and Revelation
Already in Genesis, God put a “mark [lit. a ‘sign’ (אוֹת)]” on Cain after he murdered his brother. Cain was punished, to be sure, but this sign was not the punishment. Quite the opposite. The “sign” was a shield, “lest anyone who found him should attack him” (4:15). What this mark was or where it was placed on Cain, we don’t know, but it was a mark of divine mercy, not a curse.
Later, in Exodus, there was another “mark” or “sign.” The blood of the Passover lambs on the doors of the Israelites was a “sign [אוֹת]” so the angel of death would “pass over” their homes (12:13). Once again, this blood-sign was a mark of the Lord’s mercy. Safe behind this crimson shield, the firstborn of Israel were spared.
In Ezekiel’s vision, the Lord tells an angel to go through Jerusalem and “put a mark on the foreheads of the men” who were appalled at the idolatry of the city (9:4). The Hebrew for “put a mark” is literally “to taw a taw [וְהִתְוִיתָ תָּו],” that is, trace the final letter of the Hebrew alphabet, a taw, as a seal on their foreheads.
In Hebrew script today, the taw is ת. But in Ezekiel’s day, the Hebrew letters were written in Paleo-Hebrew script. This final letter was basically two crossed lines, either in the shape of an X or a cross. In Job 31:35, the same word is used to describe a “signature”: “Here is my signature [תָּו]! Let the Almighty answer me!”
Just like an “X” can be used today as a signature by someone who cannot write, the taw/ תָּו could evidently function that way in Job’s day.
Finally, in Revelation, the 144,000, who represent the believing community of Christ on earth, are “sealed…on their foreheads” (7:3). This forehead seal is a shield to them, so that they are safe from evil, even as the signs or seals in the OT kept Cain safe from attackers, Israel safe from the angel of death, and the believing Jerusalemites safe from divine destruction. In Revelation 14, this seal is further described as the Lamb’s “name and his Father’s name written on their foreheads” (v. 1).
Seals are used to mark ownership or authorize something. The seal means “this is mine” or “from me.” The taw/ תָּו in Ezekiel’s vision probably represented God’s signature, his “X” or “+”, to indicate his divine name. It meant, “This person belongs to Yahweh” (cf. Isa. 44:5). Much like the high priest had a golden frontlet that he wore on his forehead that said, “Holy to Yahweh,” so the believers had the divine signature written upon their foreheads (Exod. 28:36).
The Cross as God’s Signature Event
Already around 200 AD, Tertullian speaks of Christians making the sign of the cross upon their foreheads when engaging in a multitude of daily tasks. He writes, “At every forward step and movement, at every going in and out, when we put on our clothes and shoes, when we bathe, when we sit at table, when we light the lamps, on couch, on seat, in all the ordinary actions of daily life, we trace upon the forehead the sign [of the cross]” (De Corona, III).
The origins of this simple ritual, still practiced by Christians from a wide variety of traditions, are most likely are to be found in the Scriptures we just went over from Genesis, Exodus, Ezekiel, and Revelation. For many Christians, the first time the cross was traced upon them was the day they were baptized.
Pulling all of this together, we might say that the cross is “God’s signature event.” He wrote his saving name in blood upon that wood.
In baptism, that name is then written upon us. We are baptized “into the name [!] of the Father and of the Son and of the Holy Spirit” (Matt. 28:18-20). We are co-crucified, co-buried, and co-resurrected with Jesus in that water, as Paul says in Romans 6:3-4, “Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.”
Baptism is our "with-Christ" event: we die, are buried, and are raised with him in those holy waters.
Water, Word, Name, and Cross thus go together. We are sealed in baptism. The Lamb of God writes his name and his Father’s name upon our foreheads.
This is like the protective mark on Cain, only infinitely better.
This is like the shield sign of Passover blood, only far superior.
This is like the taw/ תָּו in Ezekiel, only it’s Christ’s cross not just a cross-shaped Hebrew letter.
Upon the forehead of every baptized believer is a combined cross, name, and seal. Therefore the church boldly and thankfully sings,
“All newborn soldiers of the Crucified
Bear on their brows the seal of him who died.”
(“Lift High the Cross”)