If I hadn't seen Christian posters in London, and Muslim adverts on buses in Kent, then I would say the billboard in Penn is too far. However, I think it's just a retaliation from the atheists. I know I'm getting fed up with being told how peaceful religion is, but if you look at the wars going on now not much of it is to do with atheism.
I know this post will likely be negged by religious people - I'm not disregarding your religion, but I don't want it to be rubbed in my face. I don't want to be told about it or have it advertised, and I think that billboard in Penn is emphasising it. If, as a Christian, that makes you upset, imagine how irritated an atheist gets at seeing other religious advertisements.