At the start of the night, the Sifter is shown a list of all of the whispers sent on the previous day. Only the recipient of the message and the message itself is shown.
While a Sifter is alive, players are limited to 20 whispers sent each day.
Mafia sided, definitely. If it were town sided, all the mafia would have to do is... not whisper, and communicate at night instead. If it were maf sided, town will have to be careful about not outing the PRs.
I suggest that it should be town sided. Atleast there will be some leads for the town. This will make the mafia discuss everything beforehand. Impromptu whispers just make the game a bit easier. Good idea though, I liked this one.
Mafia sided, I reckon. Seems like a fun role, I can see some interesting possibilities for messing with the mafia with it (like sending things to yourself to throw off the mafia).