I'm not sure how I feel about this. Christians like these have a martyr complex, and actively engaging them in this way only makes it worse. They do realize how unpopular they are, and that's what drives them, and my personal position is that as long as they're not getting successful at legislating anything, the best thing to do is ignore them. Most Christians, even the really hardcore ones, disagree with the WBC (due to the anti-USA stuff), so I don't think there's much of a danger of people seeing their message and agreeing with it.
I guess it all depends on what you were trying to accomplish. If it was all for a laugh, I'm all for it. Awesome job!
Outside of the inbreed sign it was, among other things, a great show of differences between crazy hateful people and others. While I generally don't engage them, I think we need to let the world see we are not them. If we don't we allow them to be the face of Americans to some extent. If it was my child's school I would be rounding up everyone I could find, especially Christians and other religious folks to show them, not in our town.
Lastly, the signs being kinder and not just people yelling as they drive by shows the kids that are brainwashed into this nonsense that there is more out there.
That's probably wise, WBC makes their money by suing people who interfere with their stupidity - a couple of the family members are lawyers. That, IMO, makes them even more repugnant - if that's even possible..