I heard about this story a few weeks back, and I thought it was pretty...yeah, whatever. This always happens. Atheists puff themselves on their whole outsider/minority status, go into the public square where religious people, for the most part, play nice, and try to shake things up. Then when religious people ding them for it, they roll their eyes and say it's funny how Christians are the biggest religious sect but always act the most put-upon.
No, it's that a lot of Atheists fancy themselves to be edgy iconoclasts and they feel their Atheism is nothing without some scathing critique of religious people. This isn't new or different. Atheists like being a minority; it means they can do and say a lot of messed up shit in the name of open-mindedness, and nobody can really call them out on it because all they have to do is point to their small numbers.
I'm sorry, but their sign wasn't Atheistic, it was anti-theistic. It wasn't, "we find fulfillment in non-faith-based, non-reverential logic", it was "you're all a bunch of suckers for believing in fairy tales." They wanted attention and they got it. I don't feel sorry for them.