Currently there is no way to check if "your" hint is still shown, or a new one has overwriting it.
Or when you want to hide your hint early - but atm you may close another hint if yours has been replaced already.
Suggested implementation:
_hintData = currentHint;
_hintData contains
_id <number>: each hint[C/Silent/Cadet] sqf command execution would return an unique incrementing id
_message <string>: returns the currently displayed hint message - alternative to _id if not feasible
_type <string/number>: returns the type of hint shown (hint[C/Silent/Cadet])