A TWR GND CTLR RPTS THAT HE MAY HAVE CROSSED AN SMA WITHOUT PROPER CLRNC; OR POSSIBLY THE SMA CROSSED THE RWY WITHOUT ANY CLRNC.

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I WAS WORKING GND CTL AT BAF TWR. SMA X LANDED ON RWY 20 AND EXITED ONTO TXWY VICTOR. I LOOKED OUT AT VICTOR AND NOTICED THAT SMA X HAD CROSSED THE HOLD LINE FOR RWY 20 CORRECTLY; BUT THEN CROSSED THE HOLD SHORT LINE FOR RWY 15/33. I WAS UNSURE OF THE PLT'S INTENTIONS (I.E.; TO HOLD SHORT OF 15/33 ALBEIT OVER THE HOLD LINE; OR TO CROSS RWY 15/33). THE PLT HADN'T CALLED ME YET; BUT I IMMEDIATELY CALLED THE ACFT AND INSTRUCTED THE PLT TO HOLD HIS POS. THE PLT HEARD ME AND STOPPED. I THEN ADVISED HIM HE HAD CROSSED THE LINE; AND FOR FUTURE REF; HE MUST REMAIN BEHIND THE HOLD LINE FOR THE RWY HE WILL BE XING. THE PLT THEN MADE A 180 DEG TURN TO REPOSITION BEHIND THE HOLD LINE. NOT WANTING TO COMPLICATE THE SIT; I ADVISED THE ACFT THAT REPOSITIONING WASN'T NECESSARY AT THAT POINT AND TO JUST HOLD HIS POS. PRIOR TO THIS; I TAXIED AN SMA Y TO THE RAMP. I ALSO NOTICED SMA W ON FINAL FOR RWY 33 AND THAT PROMPTED MY IMMEDIATE ACTION(S) WITH SMA X. THE LCL CTLR HAD SEEN SMA X MAKE ITS 180 DEG ON VICTOR; WHILE DOING HIS RWY SCAN PRIOR TO CLRING AN ACFT TO LAND. HE SAID HE SAW SMA X HOLD HIS POS AND HE THEN WENT BACK TO WATCHING HIS OTHER TFC. SHORTLY AFTER THE INITIAL XMISSIONS WITH SMA X (WHILE HE WAS ON VICTOR); AN SMA Z EXITED AT CHARLIE TXWY; CALLED ME AND ASKED FOR TAXI INSTRUCTIONS TO TRANSIENT PARKING. I WAS LOOKING AT SMA Z AND I BELIEVE I INSTRUCTED THAT PLT TO TAXI TO THE RAMP. ABOUT THAT TIME; I WAS DOING OTHER TASKS AND HAD MY ATTN DIVERTED FROM SMA X ON VICTOR; WHO I LAST SAW HOLDING SHORT OF RWY 15/33. ONCE I SAW THAT THE LCL CTLR HAD NO ACFT LNDG ON RWY 33; I BEGAN TO COORDINATE FOR XING SMA X TO CROSS RWY 15/33 FROM VICTOR TXWY TO CHARLIE TXWY. I LOOKED UP AND SAW SMA X WAS GONE FROM VICTOR. AFTER LOOKING ALL AROUND THE RAMP; I SAW SMA X PARKED BELOW THE TWR AT AN FBO; AND ITS OCCUPANTS WALKING AWAY FROM THE ACFT. BELIEVING A RWY INCURSION HAD OCCURRED; I CALLED THE FBO AND HAD THE PLT CONTACT ME IN THE TWR TO GATHER NECESSARY INFO. WHEN I EXPLAINED WHAT HAPPENED; THE PLT CLAIMS HE CLRLY HEARD TAXI INSTRUCTIONS FOR HIM. WITH A PLANE ON SHORT FINAL HE SAID HE WAS SURPRISED BUT FIGURED WE KNEW WHAT WE WERE DOING. HE SAID I INSTRUCTED HIM TO TAXI 'ANYWHERE HE'D LIKE.' I RECALL THAT EXCHANGE; BUT BELIEVED IT WAS WITH SMA Z. THE XING OCCURRED WHILE THE LCL CTLR AND MYSELF WERE SCANNING OTHER AREAS; AND WE HAVE NO IDEA IF RWY SEPARATION WAS LOST (HENCE A VIOLATION); OR IF THE PLT MISHEARD ME; OR IF I DID; IN FACT; GIVE THE WRONG CALL SIGN; BELIEVING I WAS TALKING TO SMA Z. THE SMA W DOING TOUCH AND GO ON RWY 33 GAVE NO INDICATION OF FLYING NEAR ANOTHER ACFT ON THE RWY; NOR DID SMA X XING THE RWY. APPARENTLY; NO EMER EVASIVE ACTION WAS TAKEN BY EITHER PLT. I BELIEVE THAT THE MODERATE TFC; COMBINED WITH THE FACT THAT WE WERE STAFFED BY 2 CTLRS ON THAT SHIFT THAT ALLOWED NO BREAKS OTHER THAN FOR SWAPPING POS MAY HAVE CONTRIBUTED TO THE POSSIBLE ERROR. IF I WERE AT FAULT; I FEEL I MAY HAVE BEEN OPERATING AT LESS THAN PEAK ABILITY. IF THE OTHER PLT WERE AT FAULT; I FEEL IT WAS A RESULT OF NOT LISTENING CAREFULLY ENOUGH TO THE CALL SIGNS BEING USED.