MLG CROSSED RWY HOLD LINE WITHOUT ATC CLRNC.

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INSTRUCTIONS BY GND WERE 'TAXI TO RWY 4 VIA INNER.' AS I APCHED THE DEP END OF RWY 4 AN LGT WAS STOPPED AT HOLD LINE 2. I STOPPED BEHIND HIM AND SWITCHED TO TWR WITHOUT AN ACKNOWLEDGEMENT. THE LGT WAS CLRED TO POS ON RWY 4 AND THEN CLRED FOR TKOF. I CONTINUED TO TAXI; STOPPING WELL SHORT OF HOLD LINE 1. AT LEAST A MIN PASSED AND TWR CAME ON ITS FREQ AND STATED 'TAXI ACROSS THE APCH END OF RWY 4 TO TXWY 'A' AND HOLD SHORT OF INTXN AB; BECAUSE I HAD CROSSED HOLD LINE 2 AND TFC WAS ON FINAL FOR RWY 4 FOR LNDG.' I COMPLETED THE APCH END XING AND EVENTUALLY CROSSED BACK ACROSS RWY 4 AT INTXN AB AND HELD AT HOLD LINE 2 UNTIL CLRED FOR TKOF. NO INSTRUCTIONS ON ATIS OR GND CTL TO STOP AT HOLD LINE 2. I DID NOT ASK WHICH HOLD LINE TO STOP AT ON GND OR TWR. NO SPECIAL INSTRUCTIONS ARE POSTED IN OUR MANUALS OR SIGNS OBSERVED AT THE DEP END OF RWY 4 TO STATE 'UNLESS OTHERWISE DIRECTED STOP AT HOLD LINE 2.' I WILL NOW ASK GND WHICH POS THEY WANT ME TO STOP SHORT OF PRIOR TO SWITCHING TO TWR EVEN IF THEY DO NOT GIVE INSTRUCTIONS; WHICH THEY SHOULD.