From "In the Divine Service"...
Sometimes Christians make the sign of the cross on themselves. What does it mean?
The sign of the cross is a symbol to remind you of the price Jesus paid for you. It is a humble confession that you are a sinner who deserves the death Jesus died for you. It is also a joyful confession that you have been redeemed and forgiven through the bloody sacrifice of God's Son.
The sign of the cross is the symbol that was traced on your forehead (mind) and breast (heart) when you were baptized. In baptism, God buried your old sinful nature in the tomb with Christ, and joined you to His resurrection as His newborn child. So you are God's baptized child. You belong to Him by His grace. You can be sure He loves you, forgives you, and gives you eternal life.
When should we make the sign of the cross? You don't have to make the sign of the cross. But you can do so, as often as you need the reminder about God's grace to you. Do it whenever you want to remember, "Jesus died for me," or "I am baptized!"
Isn't this Roman Catholic? Roman Catholics do make the sign of the cross, perhaps for other reasons. But it is a Christian gesture, and you don't have to be a Catholic to make it. Surely it is good for all Christians to remember that we are baptized and redeemed. If something is good and healthful, should we avoid it simply because others use it wrongly? Should we stop eating fish because Catholics eat fish on Friday? Should we stop baptizing because Catholics do it too? It is enough to understand the symbol and benefit from it. Martin Luther, in his Small Catechism, instructs us to make the sign of the cross every morning and night when we call on our Father in prayer.
When would you suggest using the sign of the cross? At the opening of worship or prayer, the cross can be made while calling on God "in the name of the Father and of the + Son and of the Holy Ghost," because Jesus' death on the cross opened the veil and gave us access to God. At Matins and Vespers, you could do the same at the words "Make haste to help me, O Lord," because our help is in the cross of Christ. The conclusion of the Creed, the benediction (blessing) at the end of the service, and after receiving Jesus' body and blood are other good times to remember the cross and baptism. Why? Because the faith we confess in the creed is centered on the cross. The peace the blessing promises us flows from the cross. And the Lord's Supper applies Jesus' sacrifice on the cross to you in a very personal, concrete way.
Is there a wrong way to use the sign of the cross? God's Word does not require us to sign ourselves with the cross. There is no biblical command to do it at certain times, or with particular frequency. Nor does God promise miraculous signs or material blessings through signing the cross. We should not use the cross as a good-luck charm. Nor should we feel burdened by obligation to sign the cross.
Make use of the sign of the cross as often or as seldom as you see fit. There is no need to be concerned if your neighbor uses it more or less often than you do. This doesn't mean he or she is a better or worse Christian than you. Assume that your neighbor feels a need for encouragement from the simplest sign that tells the Gospel story. Perhaps you will be encouraged as well!