I'm going to discourage players from discussing this game with eachother via PM, though I have no actual way to enforce this.
In the event that two players would have a reason to discuss things such as tactics in detail, I'll arrange something.
How does Mafia do it? I think they just say you'll be banned from playing future games for awhile if they find out, if I'm not mistaken. You can definitely have rules that require player integrity. The two thread system of Arms Race only works because of the honor code.
I remember on gamefaqs I once went overkill on trying to make it so players couldn't cheat. I used some kind of code system, it was a nomic I believed. It killed the game pretty fast.
Near as I can tell, mafia here - every mod sets their own rules. Our most commonly used rule here seems to be that once the game starts, don't talk privately to the other players in the game - that kinda presumes nobody's like in the same household or dating or has some other daily regular interaction that wouldn't work to pause, and guess talk to the mod if that's an issue and get permission or whatever to talk about non-game things. "Seriously, I gotta ask the other player to pass the mash potatoes at dinner tonight. We're roommates."
Generally folks here that wanna play mafia don't want to ruin the game. When we find out who the members of a faction are, generally game ends on the spot, and if it's an accident that's handled gently and we just move on. Never saw it be intentional.
Mafia on another site - don't talk about the game at all period once it starts. Uber period, it is a modkill if you are known to. That is mishandled in my opinion, if you're playing 2+ games at once you can't even say you are or explain something like, "Gonna be EoD for my other game tomorrow, so expect me to not be here until after 6" or whatever - is forbidden and modkill worthy, though maybe the mod waives the kill.
I'm comfortable with however Supernerd handles this game. I bet since we write history and stuff ourselves, 2+ players could have talked to Supernerd and asked to write a history that entwines. There might already be group factions, if groups had wanted to do that; some people might already have group chatter with permission if they had wanted it and thought ahead.
It probably doesn't benefit you to be known (Yes, Imp, it does! One player submitted 'I have power over those who know what my role is!' they planned for this! - I'm making that up, I speak fully OOCly of course).
So, each of our own self-benefits probably means we all want to be secret to some degree until we act otherwise.
If you have means and intention to proclaim yourself, I recommend communicate that to Supernerd. Maybe 'Ima skywrite across town at high noon in flaming red - 'Mepa protects this town!'' or 'I take out an add in that paper, full back page. "The Talamaska, we watch, we know, and we were here before the rest of you"' or whatever.
We surely have means to do whatever we wish; I don't think anyone wants to rush and ruin the game (or just their situation) to mess up the infohazard balance.
I expect anyone concerned could share whatever with Supernerd and let him handle it.
Smooth and good play, I predict. I don't see overkill here, I think we're fine.