When I read this on the front page of Yahoo Finance, I attributed the inconsistent spelling of the February holiday to carelessness:
But it could just be the result of laziness: The editors at Yahoo didn’t bother to refer to any authorities on how to spell the holiday. But they weren’t so lazy that they couldn’t come up with yet another place to stick an apostrophe:
So, is it Presidents’ Day, Presidents Day, or President’s Day? According to the federal government, the correct name is Washington’s Birthday. But there is no universal agreement on whether to include an apostrophe in Presidents Day. The only universal agreement: Be consistent.