Ooookay, I've read it. Now, a few of the things there I do have some problems with, but I don't necessarily think that they're inappropriate. The "Happy Solstice" isn't exactly an Atheist thing, it could also be seen as Pagan or Wiccan, who celebrate the Solstice, or Yule. The "myth" sign is a bit obnoxious, but there's nothing terrible about it. Honestly, it could spark a good conversation, provided everyone can keep calm and act like adults, or if you're talking to children, really get how they see things. The separation of church and state sign is something that I know people will take offense to, but again, it's not a bad thing, it's just reiterating something that tends to go by the wayside this time of year. The quote about fables and mythologies is along those same lines; nothing bad, just a quote that people will naturally take offense to, and feel like it's attacking them or their beliefs.
All in all, I guess it's a decent way to show different sides to a well-known holiday season, and at the very least, could start a few conversations. It's too bad that there will be people who are well and truly offended by them.