Well, I would have thought the two obvious places for feedback on grading of a forum post are
a) linked with the forum post - direct inline with the post itself, but at the same time, in most cases probably a bad idea because its also public for everyone else in the forum
b) linked with the grade - which means in the gradebook, along with all other grades and feedback
Personally i would have thought that any other alternative just adds an extra degree of complexity. Of course the tutor could always private message or email the student, or even talk to them face to face, but that still takes it away from the normal workflows associated with either grades or forums and probably makes it harder to track or record.