That doesn't make any sense.
Yes, it does.
The government can't treat any one set of religious beliefs differently than any other given set of religious beliefs.
If the government put up signs saying "There is no god," that would be an endorsement of atheism. Remaining secular is just refusing to pick a side.
Atheists believe in nothing, so allowing nothing religious to be displayed is an endorsement of what they believe in.
Plenty of non-religious people celebrate christmas. I do and I don't believe in god.
Now I get how you think atheism works.
To you, atheism means you get to tell everyone else how there is no god while you personally still participate in religious celebrations. At the least, this screams out you are a hypocrite. It also may say you just advocate whatever you think will forward your agenda.
I highly doubt that if Jesus was a real person he was born on December 25th.
Yeah, he couldn't have been real because there is absolutely no corroborating evidence for the historical aspect of anything in the bible. (That was thick sarcasm if you somehow didn't get it.)
It's a cultural holiday for many people, not religious.
Face it you want to pick and choose the religious things that personally benefit you, i.e. you want a day off for fun and celebration, but you don't want people putting up displays because that doesn't fit your agenda.
You can't have it both ways. Either you're an atheist or you're not, and if you are, stop celebrating religious holidays.