Over the years, I have heard a couple of stories about supposed church buses "getting away with murder". I think you would do "better" if it looks like you are a gung-ho firebreathing biblethumper, who would preach the poor officer's ears off, than if it looks like you are a meek sheep of a respectable flock. "Repent! The World Ends Tomorrow! You -- YOU -- are a Sinner! Die, infidel scum! Allah Akbar!"
About legality, I don't actually know, but I suspect that... in our society of pretty much unlimited religous freedom, you could start your own religion and paint "Josh-uah's Third Beerdrinking Church of the Holy Motherhumper" on the bus, and you would (probably) not be breaking any law. Just a guess.
About the ethics of it... I'm too biased to comment. But I'd be more concerned about the ethical standards of the officer who sees you doing something stupid in traffic, that anything else. Your idea could backfire.
But what I'm most concerned about, is... why do you anticipate being pulled over in the first place? I'd work on that, before anything else.
(And today isn't even Sunday, and I'm preaching anyway!