MLG ACFT TAXIING TO RWY 5R AT MEXICO CITY ARPT. FLC HAD DIFFICULTY LOCATING ANY HOLD SHORT MARKINGS FOR THE RWY AND POSSIBLY ENCROACHED ON THE RWY.

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ON GND CTL WE WERE ADVISED TO TAXI TO RWY 5R 'ALL THE WAY TO THE END.' ON TAXI WE WERE SWITCHED TO TWR FREQ. WHILE TAXIING TO RWY 5R; AFTER XING RWY 5L AND ITS HOLD SHORT LINE THE CAPT TAXIED VERY SLOWLY TRYING TO FIND THE HOLD SHORT LINE FOR RWY 5R -- NEITHER ONE OF US SAW A LINE. THE ONLY LINE WE SAW WAS A SINGLE DASHED LINE AT A TXWY INTXN. THE TXWY TURNS TO GO DIRECTLY DOWN THE CTRLINE OF RWY 5R. WE DID NOT SEE ANY HOLD SHORT LINES SO THE CAPT STOPPED THE ACFT; AT WHAT APPEARED TO BE THE ACFT'S NOSE ON THE L ROW OF RWY LIGHTS. IT'S HARD TO SEE BECAUSE OF THE DISTANCE TO THE RWY -- THERE'S THE LENGTH OF THE TXWY THEN A DISPLACED THRESHOLD THEN THE RWY. DUE TO THE ODD NATURE OF THE TXWY SIT THERE NEEDS TO BE MORE MARKINGS. THE STANDARD ICAO MARKING FOR ONE AND A LIGHTED SIGN OR AMBER HOLD SHORT LIGHTS ON EITHER SIDE OR IN GND. I DO FEEL THE CTLRS DID THEIR JOB WELL AND COULD SPEAK ENGLISH WELL. THE PROB IS ARPT MARKINGS. HAD WE NOT BEEN VERY CAREFUL; IT WOULD OF BEEN VERY EASY TO TAXI ONTO THE EXTENDED CTRLINE OF THE RWY.