تعريف ومعنى "a question mark [hang] over {sth}"

What is the origin of the idiom "a question mark hangs over something" and when to use it?

The idiom "a question mark hangs over something" is used to express that there are unresolved issues, ambiguities, or unknowns related to the subject in question, and these factors cast doubt or ambiguity over the matter. The phrase originates from the literal image of a question mark, which represents uncertainty in written language.