I came across Church Signs Across America in the bookstore yesterday, and was mesmerized. The signs are a real American phenomenon, and give an interesting slice of American culture. The messages range from patronizing to punny, from inspiring to idiotic, but they are fascinating.
As it turns out, there are other books like this one (see below), as well as a couple of books with advice on the use of church signs, and sample messages. As Spock would say, "fascinating."