The sign of the cross that catholic make before a prayer or reading bible or any activity is an out word profession of faith.
The sign of the cross is a prayer,blessing,and a sacramental, as a sacramental it prepares an individual to receive grace and disposes one to cooperate with.
Also catholic believe that the sign of the cross set them apart and marked them as chosen people.
The sign of the cross is a constant reminder of the mystery of sin, the cross and salvation.
what also I want to tell you that not only the catholic cross before praying also orthodox , it's not strange in my country for Christians no matter if you are catholic or orthodox when we pass in front of a church we cross, It's also faith and love and respect to Jesus.
In my country when we cross before any Christian activity or before we pray or if we pass in front of the church it's a kind of faith no matter if we are catholic or orthodox.