I've installed a forum plugin to mark topics as "solved". This will allow us to mark contribution topics as solved while keeping the discussion open. The author of the topic may also mark the topic as solved. A tick will appear next to solved topics.
I haven't decided which other categories (if any) besides Contributions and should be able have topics that can be marked as solved, since other topics are often more of a free flowing discussion. But there may be some value in, say, marking a question about Panzer Dragoon as solved.