One use of the question mark: when implying the general from the specific.
It's common in cryptic clues to imply (a) the specific from the general - eg 'drink' to give 'ale' - and (b) the general from the specific - eg 'ale' to give 'beer'. But there's a rule for the latter: it should be accompanied by something like 'for example' or 'say' or a question mark. Hence my comment about the Clueless clue with '2020' to lead us to 'leap year'.
For yours, it would imply something cunning/cheeky - IMHO!