Once we’re nitpicking, you guys do realize that aside from the purpose of Groundhog Day (determining the weather based on whether an animal sees its shadow) would seem to be a clear issur d’oraysah, it also happens to mark an obscure, but nontheless real, religious holiday.
More substantively, Volvie, obviously there’s a difference between observing negative a commandment more scrupulously on Do Not Steal Day than focusing on your mother on Mother’s Day. There is a National Day of Prayer, would it be inapporpriate for me to express my hakaras hatov on that day to Hashem for enabling me to live somewhere where I can freely practice my religion (honestly, I’d never considered doing it, but I can’t see what would be wrong with it)?