I fear these campaigns will have a counter-effect. I believe it's pointless to say "you're wrong - we're right" because it's not an argument. I think it generates anger rather than igniting a challenging thought process.

Of course, putting forth challenging arguments on a billboard isn't an easy task. Presenting atheism in a good light rather than as an attack on religion might, however, lower their guards.

The thought provoking quote attributed to Epicurus that's been all over the internet lately should be great, albeit a bit long:

"Is God willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil? Is he neither able nor willing? Then why call him God?"