Just put it in the bounty box
There!
Should we allow such advertisements about bounties, and to what extent? Where should this information be put, and how should it be indicated?
So, to me, this seems already present in the system and such information should not belong in the body of the question.
If you feel this field is too limited in terms of revising, formatting, etc., then this should be a feature request on MSO. I do think this message could be improved in terms of visual attention. Its fixed formatting is currently easily overlooked.