Christmas a myth. Although the billboard encourages celebrating "reason", the atheists who put it up are ignoring reason. Christ's existence is a historical fact, documented by historians of the time, such as Josephus. Unless the atheists want to believe that Jesus came down to Earth as an adult, by supernatural means (and I don't think they do), then he had to have been born. So I fail to see the "reason" in this call to deny Christ's birth.
If we are free to ignore historians and believe what we want, as the atheists are advocating, why not deny the holocaust? Oh but wait - that would be hate speech. I wonder what will happen when they deny that Mohammed was born?
Then again, perhaps we are getting close to just that sort of historical relativism, when 2/3 of Canadians believe that religion is a force for evil (granted they were Canadians who had come to see Christopher Hitchens).