I didn't think the existence of such signs was a contested bit of history. I guess you can find apparently qualified people espousing all sorts of nonsense.
There are people denying the holocaust. An event for which plenty of historical evidence exists. People will believe what they want to believe.
Indeed. That is exactly the example that popped into my head as well. It would not surprise me at all if there were even a few holocaust deniers with PhDs in history.