From the Mafia rules topic:
So, for game topics like Mafia, there isn't really much point to other users posting, but they can be fun to watch, especially if you were in the game and died -- you want to see how your team fares.
With that in mind, how about implementing spectator topics? The idea being that, while anyone can read it, only the allowed users can post in it. Similar to how mods can post in closed topics, but for non-mods instead. (obviously mods could still post in these topics, because mod powers).
This is something I've thought of before, but now that there's an official mafia rule, this feature makes sense.