ACR PLT USES NON STANDARD PHRASEOLOGY WHEN USING CALL SIGN RESULTING IN THE CTLR ASKING THE PLT 3 TIMES REPEAT ACFT CALL SIGN. THE ACR PLT CONTINUED USING THE CONFUSING CALL SIGN WHILE IN THE CTLR'S AIRSPACE.

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WHILE WORKING INTERMEDIATE ALT AIRSPACE N OF ATLANTA; I WAS MODERATELY BUSY WITH 7-9 ACFT. MOST OF THE ACFT WERE EITHER DEVIATING FOR WX OR TRANSITIONING TO HIGHER/LOWER ALT. ACR WWWW WAS NBOUND AT FL310 AND ABOUT TO ENTER THE AIRSPACE. I HEARD AN ACFT CALL TO CHK IN; BUT I DID NOT UNDERSTAND THE CALL SIGN AND ASKED THE PLT TO SAY AGAIN. AGAIN I ASKED THE PLT TO REPEAT; AND I THOUGHT I HEARD ACR XYZ. SINCE I WAS NOT EXPECTING ACR XYZ; I USED THE COMPUTER TO SEARCH FOR ACR XYZ WITHOUT SUCCESS. AFTER FAILING TO LOCATE THE ACFT; I ASKED THE PLT TO SAY AGAIN ONE MORE TIME. THIS TIME THE PLT ANSWERED WITH 'ACR WWWW' AND I ACKNOWLEDGED HIS XMISSION. LATER I FINALLY REALIZED THE PLT HAD BEEN CALLING HIMSELF 'ACR FFFF.' HE CONTINUED TO USE THIS CALL SIGN THROUGHOUT MY SECTOR AND AT LEAST THE NEXT SECTOR. OF COURSE; I'M WELL AWARE THAT PLTS ARE NOT REQUIRED TO USE STANDARD PHRASEOLOGY (AS CTLRS ARE) BUT THE CONFUSION; DELAY; AND EXTRA XMISSIONS NEEDED TO LOCATE AND IDENT THIS ACFT WERE MOST UNWELCOME.