It is common in the Catholic Church to make the sign of the cross when praying and other important, specific instances during mass. Nowhere in doctrine does it specify that one has to make the sign of the cross when passing a Catholic church or emergency, though my grandmother does. She replied when I asked her about her doing this with, “It is what Catholics do – we…or I guess my family at least…have always done this…we show that we are Catholic as a reminder not to other people, but to ourselves.”
I can agree with this, but will also point out the variation and deviation from doctrine involved in religious practice that is present. It may be another example of seeking agency against the structure of a dominant religious denomination. Either way, as with belief in ghosts and aliens, we see people choosing to act as they wish and believing what they want, even if it is in contrast to or modified from the norm. Again, I will suggest it is an attempt of individuality and identity creation.