In the 2-disc version I have there's a documentary about the horror movies of Universal. One film mentioned (I think it was a silent film) was something called The Laughing Man or something like that. This man is disfigured since childhood with a permanent grin on his face. But what really struck me every time I looked at him was that he was a dead ringer for the Joker in Batman. I couldn't help but wonder if by some slim chance this was an inspiration for the Joker's appearance.
You're right on target. According to Bob Kane and others, the Joker was at least partially inspired by Conrad Veidt in THE MAN WHO LAUGHS . . ..