Noun
a punctuation mark (?) placed at the end of a sentence to indicate a question
Source: WordNetIn all affairs it's a healthy thing now and then to hang a question mark on the things you have long taken for granted. Bertrand Russell
A tired exclamation mark is a question mark. Stanisław Jerzy Lec
It meant nothing to him any longer, only a faint tinge of sadness--and somewhere within him, a drop of pain moving briefly and vanishing, like a raindrop on the glass of a window, its course in the shape of a question mark. Ayn Rand
The reason there's a question mark on my front door is just in case I forget my address. Leslie Nielsen
Whenever I start a novel, I'm always looking for two things: a bit of science that makes me go 'what if?' and a piece of history that ends in a question mark. James Rollins
Sex is a big question mark. It is something people will talk about forever. Catherine Deneuve