In my Protestant church, its easy to walk into the room, shove my hands in my pockets or grab a cup of coffee. Its easy to wander over to the snack table & start talking to someone I know. Kneeling or bowing doesn't even cross my mind because there's nothing to kneel or bow to. In prayer & the reading of the Bible, any number of us may bow our heads or close our eyes, but no other sign of solidarity is usually given. Instead, in some unspoken way, we seem to understand why we're there: we are Christians, this is our community, & this is what we do because we are "free".
If I walked into a Catholic church, everyone would know me by this same silence. I don't think I could remain anonymous for very long. I suppose I could go through the motions just to fit in, but why bother? I would be known by my fruit soon enough. However, if I were to believe I was in the actual presence of God when I walked into church, if I were there out of true reverence for God, I think I would feel very humbled. The Sign of the Cross, bowing toward the altar or kneeling- these things are acts that have the potential to mortify me, & perhaps rightly so. I would be expressing my faith for all to see & revealing that I too am in need of a Savior, I too am in need of the community of faith to make this journey with me.