Thanks for the Mother's Day info! I did further research and the British use the style of omitting the apostrophe if the word means "for." For example: Girls school. (A school for girls, as opposed to the school belonging to the girls.)
In the US there is controversy over every apostrophe placement it seems. I'm guessing that eventually we will ditch the apostrophe.
If you really want to go crazy, try and figure out where to put the apostrophe or not for Presidents' Day. What is Presidents' Day? When I grew up there was Lincoln's birthday and Washington's. Then they combined them in to "Presidents' Day."
Today, it seems, that holiday includes all presidents that ever lived. I think technically, on the books, it's only legally Washington's birthday still. But I don't have the patience to read about it again. It's so confusing.
Never mind where the apostrophe goes, I'd settle for finding out exactly what the holiday Presidents' Day is celebrating. I challenge anyone to find concrete evidence. It's up for interpretation.