If diving with a large group and diving "as a group", I´d go with the "ok" light signal approach, it´s easy and it helps keep everyone in a "team mindset"...it also works for all diving, I did a few wreck dives with a group of 5(3 that I´d never dived with before) and we managed to get thru engine-rooms and all manner of obstacles while still maintaining contact, just by using our lights...it requires good lights but I´m guessing you have that anyway...
If you want to reduce the "number of ok´s", the leader can just make an "ok" and then keep the light "in the middle" of the "ok" and just have the rest of the group "ok" around it (everyone counts the number of ok´s), and it works while moving because the "bulls eye" of your light moves with the team...or just make each diver responsible for ensuring that he get´s an "ok" from the person behind him and responsible for signalling "attention" if he doesen´t ...
even when I just have one buddy(and we have passive light communication) I like to exchange ok´s every once in a while just to keep "the conversation going"...
