Failing the standard CB radios we find on 1984 and later FLHT and above models, try the old standard hand signals.

This is a club standard, and they vary club to club.  One signal means "We're turning right in 1/2 mile."  Another means "EMERGENCY STOP!"

Here is the list of signals your club will want to develop.

Left/right turn, emergency (whole pack pulls off), emergency hassle (pre-selected individuals pull out of the pack to deal with a specific issue), emergency stop (swerve if necessary to avoid a collission), road guards out (they block traffic from cross streets and rejoin the pack), fuel up (next exit all riders re-fuel), routine break (usually at a sufficiently rowdy biker bar) and other signals to be arranged.  Make sure that if you are in the lead, you can see the other members in your club in your mirrors as they pass signals forward, and if you are in the back of the pack, pass the signal back once you see the leader make the signal. 

Be sure that everyone in your club knows all the club signals.  It is as important as your friends in the club doing the expected pre-trip inspection of your bike as you pre-trip theirs.