Once there was a man who was taught to pray by using only one phrase. For his prayer time he spoke the following in a quiet yet respectful voice; “Jesus, your will, not mine.” He spoke the words everyday for over three years until one day his actually listened to them with his heart. After that day, he never bothered to use his vocal chords in saying this prayer, he merely spoke to Jesus from the depths of his heart.
To answer your question, by making the sign of the cross and SAYING the words you are reminding yourself that you are indeed in the presence of Christ. But until you say it with your heart, you will never truly UNDERSTAND what it means to actually be in the constant presence of Jesus.
