The signs were an effort to reach out to other atheists and skeptics, and let them know that even though they lived in the Bible Belt they weren't alone. The signs would stay on the buses for a few week (actually they could afford to put them on only four buses) and probably reach only a limited number of people (since the four buses ran the same routes each day). It wasn't a huge ad campaign, but the DFWCOR was doing what they could afford to do.
But that was before the christians got involved. Evidently the fundies, who were incensed by the limited bus signs, decided that the campaign needed a much wider distribution. They tried to organize a bus boycott (which mostly failed), hired a truck to follow the buses with a sign that said, "I still love you - God", and showed up at the transportation board meetings demanding the atheist signs be removed from the buses.
It was the intention of these christian bigots to snuff out the small atheist ad campaign, but it had exactly the opposite effect. The news media (and the blogs) got hold of the story, and all of a sudden the atheist ad was being seen and read by hundreds of thousands of people (if not millions) instead of the few thousand they were hoping to reach. And it made the fundie christians look like the intolerant jerks they really are.
In addition, they kind of shot themselves in the foot. After seeing how unhappy the fundies were about the ads, the bus company has changed their policy and will no longer accept ads about religion from anyone. So to prevent the random atheist ad every few years, the fundie christians have fixed it so no religious organization (including them) can ever buy ad space on any bus.
So, a big thank you goes out to the fundie christians. They gave the atheist ads a much wider distribution, and we won't have to ever see any more religious ads on the buses. That sounds like a win-win to me.
