Thanks for your question to us here at TruthBook.
If I am not mistaken, the sign of the cross is a distinctly Catholic practice; I was raised a Catholic from childhood, and so I am more than familiar with it. We were taught to make the sign of the cross numerous times throughout the day; before meals, before prayers, and when entering or leaving a church (along with a dab of holy water!) The prayer that goes with it, as one is crossing oneself from forehead to heart, and from shoulder to shoulder, is: "In the name of the Father, the Son, and the Holy Spirit, Amen."
You want to know if it is required...required by whom? God? Surely not...I am not even aware that it is a requirement of the Catholic Church; instead it is a sweet reminder of the Trinity, and we cross ourselves with this remembrance as a sort of holy consecration of purpose for whatever follows, whether it be prayer, a meal, whatever.
If you are a reader of The Urantia Book, which you seem to be, you may be aware that God does not require ritual of any kind in order for us to connect to him; a ritual such as the sign of the cross is man-made - an outward, physical demonstration of connecting to God. But such is not necessary when praying. The sign of the cross is not necessary - in fact, words are not even necessary for prayer:
91:8.12 Words are irrelevant to prayer; they are merely the intellectual channel in which the river of spiritual supplication may chance to flow. The word value of a prayer is purely autosuggestive in private devotions and sociosuggestive in group devotions. God answers the soul's attitude, not the words.
Having said all that, though, I cannot fault anyone who wishes to incorporate this practice of the sign of the cross into their prayer-time or their religious practice. I have always thought it was a nice practice, helping a soul be grounded in spirit - reminded of God in the Trinity. But as to whether God requires it, I think it is safe to say that he does not. I am sure there is no harm in our doing it, though, if we find it helpful.
Thanks so much for writing; it is a good question...