Ok... I'm starting off easy. If you see someone make the sign of the cross you know exactly what religion he/she follows. The sign of the cross has become an outward symbol of Catholicism. However, its an easy place to start because it's not something that has to be exclusive to the Catholic church - for instance, anyone in my Baptist background could make the sign of the cross too.
The sign of the cross is simply invoking the trinity - the father, the son, the holy spirit. It's a way to make ordinary tasks (meal time, sleep, trips, meetings, etc) a holy one. Many times Catholics will make the sign of the cross before praying, receiving a blessing, entering/exiting a church, etc. But as you can see its a practice that any protestant believing in the trinity could make their own. I find it is a good way to remind myself of how awesome God really is. How can He be 3 persons/beings/states in one? It's AMAZING!
Now, there is another aspect of the sign of the cross that occurs during the Mass. Before reading the gospel, each Catholic traces a small sign of the cross on their forehead, lips, and heart. While making the three crosses a silent prayer is given, "Oh Lord bless my mind, my speech, and my heart that I may worthily hear your Word and proclaim it." I had never heard of the prayer, but instead took the purpose of this act is to remind myself that I need God to protect my mind, my lips (what I say), and my heart against the devil. I guess I wasn't too far off.
Personal Reflection: I don't have a problem with the sign of the cross. I think it is a neat way to remind myself of God's greatness, but I tend to forget about it. :) I remember at Mass because everyone else is doing it, but its not something that has become a daily habit for me. I guess this will come over time. I wonder if others who did not grow up Catholic found it hard to remember to make the sign of the cross too. (If anyone who fits this category would like to make a comment or e-mail me, I'd appreciate it)