B737-700 FLT CREW WAS CONFUSED WITH REGARD TO LOCATION OF HOLD-SHORT LINES BETWEEN RWYS 6C AND 6R AT CLE.

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WE LANDED ON RWY 6L EXITING AT TXWY R. WE WERE INSTRUCTED TO HOLD SHORT OF RWY 6R. RWY 6C WAS CLOSED. INITIALLY WE PAUSED BEFORE XING RWY 6C TO MAKE SURE WE HAD IDENTED IT CORRECTLY. THEN WE PROCEEDED TO CROSS RWY 6C. AS WE APCHED RWY 6R WE WERE UNSURE OF THE RWY MARKINGS AND MAY HAVE CROSSED THE LINE ONTO RWY 6R. WHEN WE BECAME UNSURE OF OUR POS; WE STOPPED. WITHIN A SECOND OR TWO WE WERE CLRED ACROSS RWY 6R AND WE PROCEEDED. EVEN NOW WE ARE NOT SURE IF WE ENTERED THE RWY PREMATURELY BUT WE SUBMIT THIS TO AGAIN HIGHLIGHT THE CRITICAL RWY LAYOUT IN CLE AND TO ENCOURAGE CONSTANT VIGILANCE ON THE PART OF ALL AIR CREWS WHEN OPERATING IN CLE. OF COURSE; THERE IS NO SUBSTITUTE FOR CONSTANT CREW VIGILANCE AND SITUATIONAL AWARENESS. WE CAN NEVER EMPHASIZE THIS TOO MUCH. IN ADDITION; I HAD THE FOLLOWING THOUGHT -- HAVE THEY EVER CONSIDERED USING THE CENTER RWY IN CLE AS THE STANDARD HOLD SHORT POINT FOR THE INBOARD RWY? THERE IS SUCH NONSTANDARD SPACING BTWN THESE 2 RWYS THAT NOW WITH AN ADDITIONAL OUTBOARD RWY THE CENTER AND INBOARD COULD BE CONSIDERED 'ONE' RWY FOR XING PURPOSES.