Catholicism is not a private affair... It is a way of life. There are a select few afraid of making even the sign of the cross in public... Even better reason to do it! Maybe a fallen away Catholic will be reminded by a gesture or a struggling person comforted.
"Everyone who acknowledges me before others I will acknowledge before my heavenly Father. But whoever denies me before others, I will deny before my heavenly Father".
Nervous? Perhaps pray with others or simply pray silently. We will not be punished for our less-than-eloquent prayers either. God loves us with an uncompromising love.
Focus on talking to God and forget about trying to move or impress everyone else. Your prayer will be sincere and God (who's opinion is the only one that matters on this subject) will be pleased.
Remember, you can do all things through Christ who strengthens you.
Lord, teach us to pray... In this case... Publically.