I guess if it brings some people peace and happiness than I don't see the harm. I agree that it looks like a thumb though or at least a finger pointing. Our world is so serious that people seek out things to calm them down. As a Catholic, I think it is cool that people get some happiness out of it.
God Bless these people of simple faith. If it brings so many hundreds together in prayer, it's a good thing. I wish I could have that childlike faith again.