Before the liturgical reforms of Vatican II was required to cover, with purple veils, all the crosses and images displayed to the church service. In the Roman Missal of S. Pius V, after the Mass on Saturday preceding the Sunday of the Passion (now Fifth Sunday of Lent), was the heading: "Before the Vespers, cover up their crosses and images which are in the church. The crosses remain covered until the end of the worship of the Cross on Good Friday, and Images to the Hymn of the Angels (Glory to God in Heaven) on Holy Saturday. " See that it was the custom on the last two weeks of Lent, through which it wished to focus the attention of the faithful in the mystery of Christ's Passion. All that could cut into it, as were the images of Saints, was covered.
Such a practice is highly encouraged even in modern Catholic Churches. Traditionalist Catholics and Anglo-Catholics still observe the ancient practice of Passiontide. Quoting from "The Catholic Source Book":
Traditionally, the Fifth Sunday of Lent, one week before Palm Sunday, was called Passion Sunday or Judica Sunday after the first word of the Introit: "Judge me, O Lord..." (see Psalm 43). The veiling referred to the closing words of the Sunday's Gospel, "They picked up stones to throw at him, but Jesus hid himself, and went out of the temple" (John 8:59). The Lenten veil expressed the sorrow of the Church at this time.CatechismClass.com offers an integrative catechism lesson for this Sunday for only $2. It is available here.