Should There Be an Apostrophe in Presidents Day?

There should be a simple answer to the question of how to punctuate today's holiday. But the problem is that Presidents Day is not the official name of the holiday; it's Washington's Birthday. But most workplaces -- including my own -- give employees the day off in honor of more than one president. So, how should we punctuate presidents?

Driving along the Auto Mile a couple of days ago, I saw it written on banners as President's Day, Presidents' Day, and Presidents Day. Option number two is what my calendar uses. But my calendar -- and this list of federal holidays -- calls November 11 Veterans Day (no apostrophe). If we were going for consistency, today should be Presidents Day. That's certainly what they'd do in Birmingham. But I'm going to have to declare Presidents' Day the winner. It just looks right.