Usually when I'm out in the world smashing things people only notice I'm multiboxing because all my characters have a similar look / same transmog. I don't hide it.

That said I drive from the healer and my melee tend to pickup whatever is available from nearest target. Then on the same rotation they assist tank > assist melee > assist range > follow master in that contingency order.

In the Pit it would just look like the DK smashing something, the warrior on something else and the hunters assisting the DK from afar. With the shaman spot healing whoever needs it.

One of the best macros I've ever used multiboxing was the one that handles assist and follow contingencies. Just uses @target and @char references to pick what to do.

People would generally approach and ask for an invite and never knew I was multiboxing. Though whenever I was in town just clumped together I would get the usual /spit or whatever the peanut gallery had to say on multiboxing.