Sign of the Cross

“IN all our actions when we come in or go out, when we dress, when we wash, at our meals, before retiring to sleep, we make on our foreheads the sign of the cross. These practices are not committed by a formal law of Scripture, but tradition teaches them, custom confirms them, faith observes them.”

~Tertullian: De Corona, 3.

“AND when tempted always reverently seal thy forehead with the sign of the cross. For this sign of the Passion is displayed and made manifest against the devil if thou makest it in faith, not in order that thou mayest be seen of men, but by thy knowledge putting it forward as a shield.”

~St. Hippolytus: The Apostolic Tradition, 42.

“LET us, therefore, not be ashamed of the cross of Christ; but though another hide it, do thou openly seal it upon thy forehead, that the devils may hold the royal sign and flee trembling far away. Make then this sign at eating and drinking, at sitting, at lying down, at rising up, at speaking, at walking: in a word, at every act.”

~St. Cyril of Jerusalem: Catechetical Discourses, 4, 14.

Crucifix, by Coppo di Marcovaldo.
Tempera on wood, c. 1261; Pinacoteca Civica, San Gimignano.