Although not usually done by Catholic churches (at least from what I've need in my travels), many other types of churches have their outdoor signs to display messages. Any cute, intriguing, or funny ones that you've seen?
The local Baptist church that I drive by everyday currently has one that says "Government making sin legal doesn't make it right".
Another one currently has one stating "Read the Bible - It will scare the hell out of you".
Last summer during a very hot spell the 7th Day Adventists had one saying "If you think it's hot here, what do you think hell is like?"