CARGO ACFT TAXIES BEYOND HOLD LINE.

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WE WERE GIVEN THE FOLLOWING CLRNC FROM GND 'CLRED TO RWY 8R; HOLD SHORT OF THE EXTENDED CTRLINE OF RWY 4R.' WHILE TURNING ONTO TXWY RA; GND TOLD US TO 'MONITOR THE TWR;' WHICH WE DID. AT THIS POINT I/CREW ASSUMED WE WERE CLRED TO RWY 8R. THE NEXT THING WE HEARD ON THE TWR FREQ. WAS 'WEREN'T YOU TOLD TO HOLD SHORT OF THE EXTENDED CTRLINE OF RWY 4R?' I TOLD THE TWR WE ASSUMED WE WERE CLRED TO RWY 8R WHEN WE WERE TOLD TO MONITOR THE TWR BY GND CTL. THE TAXI FROM OUR RAMP TO RWY 8R IS ABOUT 3 MI; ON A REMOTE PART OF THE ARPT. THE TXWY RA WAS NO XING TXWYS OR RWYS. BECAUSE OF THIS; ONE HAS VERY FEW CUES ON THIS VERY LONG AND ISOLATED TXWY; TO ALERT ONESELF OF ONLY A PAINTED HOLD LINE ACROSS THE TXWY. TO PRECLUDE THIS FROM HAPPENING AGAIN; INSTEAD OF BEING TOLD TO JUST MONITOR THE TWR. GND CTL SHOULD HAVE TOLD US TO CONTACT THE TWR AND HOLD SHORT ON TXWY RA. SUPPLEMENTAL INFO FROM ACN 274659: I ALSO BELIEVE REEF TXWY AT HOLD SHORT LINE FOR RWY 4R ILS IS OUT OF VIEW OF CTLR. NEED MORE EXPLICIT INSTRUCTIONS AT HDOF POINT TO TWR. AFTER THAT HOLD POINT STILL QUITE SOME DISTANCE TO TAXI. ONLY MARKING OF HOLD POINT IS YELLOW LINES ON TXWY -- NEED SIGN.