You can add a code into the initialization line of every group leader (in this case a fireteam leader) to give all of his grouped units a specific name.
Code:
name setGroupID ["put your callsign of choice here"];
So if you use the callsign "ECHO", each unit which has been grouped to the group leader, will be called "ECHO" starting with the leader as ECHO 1, the next higher ranked unit as ECHO 2, ECHO 3, ECHO 4 and so on.
You can also have a look about High Command editing here:
1. http://forums.bistudio.com/showthread.php?t=83277
2. http://community.bistudio.com/wiki/High_Command
3. http://forums.bistudio.com/showthread.php?t=80032