With the normal sign of the cross you are supposed to say "In the name of the Father and the Son and the Holy Spirit/Ghost" as you trace the cross on your body.
The solemn sign of the cross is the triple cross which is made on the forehead, lips and chest. In Catholicism this happens before the priest reads the Gospel during every mass. As we make the solemn sign of the cross we say "Glory to you O lord" in the Novus Ordo (Ordinary Form) or "Gloria tibi Domine" in the Traditional Latin Mass (Extraordinary Form), but that is not the prayer which is strictly associated with the motion itself.
I'm wondering what words are supposed to be associated with the solemn sign of the cross, and if there are different words depending on your country? For example I've heard that the priest is supposed to pray silently to himself "May Christ's words be on my mind, on my lips, and in my heart" as he makes the motion, and I've heard that the congregation is supposed to pray something like "I believe with my mind, confess with my mouth, and live out in my heart, the gospel".
However I can't confirm this because google is giving me nothing and my memory is fuzzy.