its not as simple as having whatever callsign they feel like guys...
callsigns should represent what that vehicle is capable of. that way it is simple for any brigade (that may not be neighouring) to see an appliance and know what they can expect from it.... every appliance has little bits n pieces added to it, the callsign doesnt neeed to reflect this.
however, if an appliance is an RCR resource (a real one like aldinga's, not seaford's 24p for instance (no not slagging seaford so calm down...) then IMO it should be labelled either "pumprescue" if it has a fire fighting capability, or "rescue" if its a dedicated...
see... easy for all. then there are the other callsigns that already make sense, 24P, 34, 14, etc....