I have thought of an idea which might be helpful, oddly enough, for a forum just like this - the requests forum. I run a requests forum myself, and I like to use topic icons to mark the requests for my own convenience - one icon means completed, one means rejected, one means accepted to do etc. But I have to keep reminding the posters not to apply message icons to their own messages, because it confuses me. It would be extremely useful if the use of message icons could have user permissions applied to it, especially on a per-board basis.
we would need such a functionality as well.