The early Christians saw in Ezekiel 9:4 a prophecy of the sign of the cross. Ezekiel 9:4 in the Greek reads, “Go through the midst of Jerusalem, and set a mark (Greek letter tau) on the foreheads of the men that groan and that grieve for the iniquities that are done in the midst of them.” The Greek letter tau is the same as our T, which is in the shape of a cross.
Making the sign of the cross is a very ancient practice of Christians. It is made to remind us of our baptism, as a sign of blessing, a sign for protection, and also a sign against the demonic.
It’s a beautiful practice that everyone should make a part of their devotional life.