There is actually quite a lot in Scripture about the Mark of the Beast. These are quoted from the NKJV.
Rev. 13: 16ff He causes all, both small and great, rich and poor, free and slave, to receive a mark on their right hand or on their foreheads, 17 and that no one may buy or sell except one who has the mark or the name of the beast, or the number of his name. 18 Here is wisdom. Let him who has understanding calculate the number of the beast, for it is the number of a man: His number is 666. Rev. 14: 8ff And another angel followed, saying, “Babylon is fallen, is fallen, that great city, because she has made all nations drink of the wine of the wrath of her fornication.” 9 Then a third angel followed them, saying with a loud voice, “If anyone worships the beast and his image, and receives his mark on his forehead or on his hand, 10 he himself shall also drink of the wine of the wrath of God, which is poured out full strength into the cup of His indignation. He shall be tormented with fire and brimstone in the presence of the holy angels and in the presence of the Lamb. 11 And the smoke of their torment ascends forever and ever; and they have no rest day or night, who worship the beast and his image, and whoever receives the mark of his name.” 12 Here is the patience of the saints; here are those who keep the commandments of God and the faith of Jesus. Rev 20: 4ff And I saw thrones, and they sat on them, and judgment was committed to them. Then I saw the souls of those who had been beheaded for their witness to Jesus and for the word of God, who had not worshiped the beast or his image, and had not received his mark on their foreheads or on their hands. And they lived and reigned with Christ for a thousand years. 5 But the rest of the dead did not live again until the thousand years were finished. This is the first resurrection.
In Romans 13 the Apostle Paul tells us to ‘put on Christ’ 13 Let us walk properly, as in the day, not in revelry and drunkenness, not in lewdness and lust, not in strife and envy. 14 But put on the Lord Jesus Christ, and make no provision for the flesh, to fulfill its lusts.
Since the earliest Church, Christians have ‘put on Christ’ in the form of a sign, as signs are extremely important in salvation history, not only for the Israelites that came before, but also for Jesus and His apostles.
The sign that ‘puts on Christ’ has been making the sign of the cross, and in both branches of the ancient Church, and in all the branches from there, Christians make the sign of the cross with their right hand, from the forehead, to the solar plexus, then shoulder to shoulder. This is the sign they use to begin and end prayer, by ‘putting on Christ’ they are accessing His power to save, His relationship with God, His intercession that was obtained for us by His sacrifice on the cross.
The mark of the beast is either on the forehead or hand, which subsumes the sign of the cross to the sign of the anti-christ. With that chip implanted in the hand, it is a defiled hand that rejects the cross making that sign. With that chip implanted in the forehead, it would be the FIRST thing touched when making the sign of the cross, subsuming the sacrifice to the anti-christ.
Amazing how that works. Just notice how badly God takes it.