Sign of the Cross and Dr. Martin Luther
Futher evidence that a "non-biblical" devotional practice can still be used by Protestant and Catholic alike comes from the father of the reformation, Dr. Luther himself:
"Such external things as confession, bowing our knees, making the sign of the cross mark no distinction between Protestants and Roman Catholics
Luther himself went often to confession, he bended his knees both at home and in the church, and in his little catechism he suggests that a Christian should make the sign of the cross both morning and evening."
"Just because something is done in the Roman Catholic Church doesn't mean it should be cast aside by evangelicals"
From Confessing Evangelicals Blog