ACR FLT CREW REPORTS CONFUSION IDENTIFYING THE RUNWAY AT MIA DURING TAXI FOR TAKEOFF.

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CLRED TO TAKE OFF ON RWY 27 FROM Q8. AS I LOOKED DOWN THE RWY FOR THE NUMBER 27 TO CONFIRM POS PRIOR TO TURNING DOWN THE RWY; I COULD NOT SEE THE NUMBER AS I WAS ON THE DISPLACED THRESHOLD BUT I SAW A RED SIGN THAT SAID 30-12. I LOOKED TO MY L TO CHK THE OTHER RWY AND I SAW A SIGN THAT SAID 27-9. I THOUGHT FOR A MOMENT THAT 27 WAS TO MY L. AS I CONTINUED ALONG TXWY Q8 I REALIZED MY MISTAKE AND STOPPED THE ACFT. ABOUT THEN TWR CALLED AND SAID YOU MISSED YOUR TURN. AT THIS TIME THE BACK HALF OF MY ACFT WAS STILL ON RWY 27. THE TWR SAID HOLD YOUR POS THEN ASKED IF I WAS OVER THE 30 HOLD LINE. I WAS UNSURE OF MY POS RELATIVE TO THE 30 HOLD LINE SO I TOLD TWR I WAS OVER IT; THOUGH IN RETROSPECT I MAY HAVE NOT BEEN. TWR THEN CLRED US FOR TKOF. I REALIZE THIS WAS A VERY SERIOUS ERROR AND SHOULD NOT HAVE HAPPENED. WE BOTH HAD OUR MAPS OUT; I AM FAMILIAR WITH MIA AND I KNOW THOSE SIGNS INDICATE RWY YOU ARE APCHING; BUT I WAS LOOKING FOR CONFIRMATION OF THE PROPER RWY BEFORE I TURNED DOWN AND LINED UP. WHEN I SAW THE 30 ON MY INTENDED RWY AND 27 TO MY L IT CONFUSED ME JUST ENOUGH TO CAUSE THE ERROR. I THINK FATIGUE WAS A FACTOR AS WE HAD A VERY EARLY WAKE UP. SUPPLEMENTAL INFO FROM ACN 767501: IT IS VERY DIFFICULT TO DETERMINE THE RWY WITH REF TO THE TAXI SIGNS. I WOULD RECOMMEND THE TYPES OF PAINTED RWY MARKINGS FOUND ON EUROPEAN RWYS TO AVOID THIS CONFUSION.