I don't agree with the OP, keep the mods identities private. If we can email and get an explination or mroe info, that should be good enough.
At most, an automatic email or in-game message could be sent when a mod bans someone, citing a reson or a moderator ID #. Moderator ID #s I think might help relieve some people's distrust of the confdentiality of the mods, or some form of ID that can be attached to each mod without revealing their in-game or forum ID. This could also be beneficial because a mod could then elect to broadcast an arena-wide message, ie: "HTCMod#5: 200: Last warning guys, next politicaly related remarks get AT LEAST a 3-day mute". Don't have these mods not show up on any list or roster though, that way people can't tell if they're on or not (or AFK).