MEM LCL CTLR EXPRESSED CONCERN REGARDING BOTH FAA AND ARPT MAINT VEHICLES THAT UTILIZED QUESTIONABLE RADIO IDENT.

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WHILE WORKING THE LCL CTL #2 (LC2) POS DURING THE MORNING INBOUND. I OBSERVED AND OVERHEARD A DANGEROUS SITUATION INVOLVING FAA MAINT VEHICLES COORDINATING THEIR MOVEMENTS WITH GND CTL #2 (GC2). THERE WAS TRAINING ON THE GC2 POS WHEN 'FAA MAINT' CALLED GC2 AND REQUESTED PERMISSION TO PROCEED FROM THE CARGO RAMP TO THE RWY 36C LOC SITE. THE TRAINEE INSTRUCTED 'FAA MAINT' TO 'PROCEED AS REQUESTED.' SEVERAL MINS LATER 'FAA MAINT' CALLED AND REQUESTED TO PROCEED FROM A DIFFERENT LOCATION (NOT THE RWY 36C LOC SITE) TO THE RWY 18C GS. THE TRAINEE THOUGHT THAT THE DRIVER OF 'FAA MAINT' WAS CONFUSED; AND INSTRUCTED 'FAA MAINT' TO 'PROCEED AS REQUESTED.' WHAT WAS UNKNOWN AT THE TIME; WAS THAT A SEPARATE FAA VEHICLE WAS OPERATING ON THE AIRFIELD USING THE SAME 'FAA MAINT' CALL SIGN. THESE VEHICLES USUALLY APPEND A NUMBER AT THE END OF THEIR CALL SIGN LIKE 'FAA MAINT 123.' A SECOND VEHICLE THEN APPEARED ON THE AIRFIELD FROM ANOTHER LOCATION; AND THE TRAINEE AND TRAINER THEN REALIZED THAT THERE WERE 2 VEHICLES OPERATING FROM 2 DIFFERENT LOCATIONS; AND UTILIZING THE SAME CALL SIGN. ALL VEHICLES NEED TO USE UNIQUE CALL SIGNS FOR THEIR OP; NOT JUST 'FAA MAINT' OR 'AIRFIELD MAINT.' APPENDING A NUMBER AT THE END OF THE VEHICLE'S PRIMARY FUNCTION WILL ALERT THE CTLR OF DIFFERENT VEHICLES AND THEIR SPECIFIC REQUESTS. THE OUTCOME OF THIS COULD HAVE BEEN VERY DIFFERENT HAD ONE OF THESE VEHICLES CROSSED AN ACTIVE RWY IN FRONT OF ARRIVING OR DEPARTING TFC.