A creche? Religious. Menorahs and the Star and Crescent? Secular.

At least that's how the New York City public school system sees things. They will allow "secular" holiday symbols like "Christmas trees, Menorahs, and the Star and Crescent" but not "religious" symbols like a nativity scene. (Read more about this here and here.)

Does this make any sense? Actually yes, if your desire is to somehow prohibit explicitly Christian symbols while permitting symbols from other traditions.