While I was raised in a Catholic family, I don't know the customs of today. In the days of yore, one made the sign of the cross with the phrase, in the name of the father, the son, and the holy ghost. The sign of the cross was intimately connected with the Trinity. As for the false prophet Paul joining the imagery of the cross with salvation, such as in his false gospel of the cross/grace, well, those who follow the ravaging wolves, wind up on the path to destruction (Matthew 7:13-15). As for the story of Milvian Bridge, I suspect Eusebius, as the court historian, made up both versions. The first being around 312 AD, 1 year prior to Constantine minting his sun god coin, and another once Constantine started pushing his new Roman church. As for Constantine being baptized, that story would have been written by Eusebius, an Arian, and once he mentioned that history was often not true, written falsely for the good of the little people.