how do I tell when people are talking in character, as opposed to when their players are talking?
In any place except the Mun Loft, all conversation made is assumed to be on the part of the character. For example, anything said in the village square is pretty much assumed to be said on the part of the character Commoner Whatshisname, and not the player behind the computer. If you want to say something, as a player, the best way to convey this is through the use of OOC bubbles like this. ((These bubbles are a sort of symbolization used in various online RPs to let a player say things without breaking the suspension of disbelief on the part of the characters.