Unbelief means you don't believe. It doesn't mean you can't have other opinions. I don't object to displays just because they're religious, they have to also be on government property. I think the school isn't doing anything illegal, I'm just no more surprised about atheists complaining about it than I would be about Christian parents complaining about their kids being taken to a mosque. The value of keeping government and religion as separate as possible suddenly becomes apparent to Christianists when it's a different religion getting the advantage.