St. Hippolytus: "The sign of the Cross"

"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 makes 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 of Rome: The Apostolic Tradition, 37.1.

Pope Francis