Occasionally, we get questions on main taken from old contests, such as Olympiads and Putnam exams. These questions are inappropriate for MO, and they get closed, which is as it should be. However, before they get closed, they sometimes get comments along the lines of $$\rm Do\ your\ own\ homework.$$ It's usually not that hard to tell a homework question from a contest-type question. People who are posting contest-type questions are showing an interest in Mathematics beyond passing the course they are enrolled in, and I think we should be encouraging their continued interest in Mathematics (or at the very least, not discouraging it). I don't think "Do your own homework" serves this purpose. I'd rather see a comment along the lines of, $$\rm Nice\ question!\ But\ not\ suitable\ for\ this\ website.\ Try\ Art\ of\ problem\ solving,\ or\ math.stackexchange$$ 

So, may I suggest that 1) if we leave any comments on contest-type questions, they be encouraging comments, and 2) if we see rude comments on contest-type questions, we flag the comments for moderator attention?