ACR STARTED TO CROSS RWY WITHOUT CLRNC. UNAUTHORIZED RWY ENTRY.

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WE WERE INSTRUCTED BY CLE GND TO TAXI TO RWY 23L FOR DEP. I BELIEVE THAT THE CAPT HAD HIS R AND L MIXED UP AND THOUGHT HE WAS GOING TO 23R WHEN HE CROSSED THE HOLD LINE. I STATED 23L WHEN HE CROSSED THE LINE AND SAID THAT THERE WAS AN ACFT ON FINAL. THE GND CTLR SAID TO HOLD SHORT OF 23L AND TO CONTACT THE TWR FOR DEP CLRNC. AT THIS TIME THE CAPT STOPPED THE AIRPLANE AND SAID THAT HE HAD MADE A MISTAKE. WE DID STOP SHORT OF THE RWY. REGARDLESS OF WHERE THE CAPT THOUGHT HE WAS GOING; THE RWY HOLD LINE IS VERY CONFUSING FOR 23L AT CLE. RWY 28 AND 23L CROSS ALMOST AT THE APCH END OF 23L. THERE IS A HOLD LINE AND A RED SIGN MARKED 10-28. THIS LED ME TO BELIEVE THAT IT WAS THE RWY 28 HOLD LINE. I DO NOT RECALL SEEING A RED SIGN MARKED 23L. THE RWY HOLD LINE AND SIGNS SHOULD CLRLY INDICATE THE INTXN SO THAT THIS TYPE OF OCCURRENCE IS PREVENTED IN THE FUTURE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR GAVE INFO REGARDING ACFT Y WHICH COMPLETED LNDG ON RWY 23L; EVEN THOUGH RPTR ACFT X WAS CLOSE TO RWY. SAYS THAT PIC WAS UNFAMILIAR WITH CLE ARPT. DOES NOT KNOW WHY PIC HAD RWY 23R IN MIND AS THEY TAXIED ACROSS 28. STILL NOT SURE IF THERE IS A HOLD LINE FOR 23L. WE DISCUSSED TECHNIQUE OF HOLDING SHORT OF 10/28 WHEN WAITING FOR TKOF ON 23L. RPTR HAD TO TELL PF TWICE BEFORE GETTING PF TO STOP ACFT. ACFT ON FINAL HAD NO PROBLEM COMPLETING LNDG. NO FOLLOW-UP ACTION BY FAA ON THE INCIDENT.