I really like the idea.
I really think that this should be anonymous. We don't want people voting only for their cafe's artists.
We could reveal the artists after each round, so we know who is still in it and who has been eliminated, but while the voting is going on it should be as anonymous as possible (and this means the name given to the sig so that there can be no cheating).
I will give any mod help that you need over here to keep this thing going - just send me a PM if you need any stickies, announcements etc.