Using "?-mark" with "か" particle or not?

Hi everybody,

I've been wondering since you can drop the question mark at the end of the sentence when the question particle か is used, would it be weird to put a question mark nevertheless?

AFAIK, it is not grammatically incorrect to put a question mark (correct me if I'm wrong), but would people think it is weird if I put a question mark there, since I always tend to put one out of habit.

Not weird at all. It's often used to make clear the meaning, not only after か. The meaning of a sentence can be different whether it's a question or not. For instance, 一緒に行きません is a refusal, whereas 一緒に行きません？ is an invitation. In a conversation, we can recognize the meaning from the intonaton at the end of the sentence (or from the context, of course), but written texts can't differentiate them. That's why the question mark is convenient.