Is It Presidents Day Yet?

Presidents Day is coming up and I still don't know if it's "President's Day" or "Presidents' Day." Is this the day for all Presidents through history, or is this the day to honor the guy in office? Is this like Father's Day, where we only care about one father? Or, is it like Arbor Day where we all plant trees and don't mind one specific Arborist. I once heard that Presidents Day was named in honor of Lincoln and Washington, which is why it falls at the midpoint of their birthdays. So if it's nothing more than a birthday party for them, do people who know actual Presidents have to buy them gifts? To me, this holiday is like a double down on Father's Day for all the living Presidents, and for the rest of us it simply means that mattresses are on sale. And I wonder if that's because you're supposed to buy all the living Presidents mattresses on Presidents Day?