Making the sign of the cross is something Orthodox Christians do frequently, and sometimes mindlessly. There are a number of references to this practice from the early church. The early church fathers are clearly aware of the practice, though they don’t describe the mechanics of it, so we don’t know exactly how they did it. But the power wasn’t in how it was done, but in the cross itself.
One of the earliest references to making the sign of the cross comes from Tertullian (d. 225 AD). 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. For these and such like rules, if thou requires a law in the Scriptures, thou shalt find none: tradition will be pleaded to thee as originating, custom as confirming, and faith as observing them” (The Chaplet 3).
Tertullian is defending what has been established as tradition among the early Christians. He admits that making the sign of the cross is not attested to in scripture, but no matter, for there is the living faith of the Christians: the things Christians can be observed to do. Making the sign of the cross is for Tertullian something Christians do multiple times during the course of their ordinary, daily lives.
St. Cyril of Jerusalem (d. 386AD), writing more than 100 years after Tertullian teaches the new Christian converts to continue this tradition which has come down through the centuries:
“Let us not be ashamed to confess the Crucified. Let us boldly make the cross as our seal upon our brow on all occasions: over the bread we eat, over the cups we drink; in our comings and in our goings; before sleep; on lying down and rising up; when we are on the way and when we are still. It is a powerful safeguard; it is without price, for the sake of the poor; without toil, because of the sick; for it is a grace from God, a badge of the faithful, and a terror to demons; for “He made a public display of them, triumphing over them in the cross” [Col 2:15]. For when they see the cross, they are reminded of the Crucified.” ( A Patristic Treasury: Early Church Wisdom for Today, Kindle Loc. Loc. 3498-3503)