CAPT OF ACR MDT ACFT INADVERTENTLY TRANSGRESSED A RWY DURING TAXI FOR TKOF TO WHICH INSTRUCTED TO HOLD SHORT.

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PRIOR TO START AND TAXI FOR DEP; WE (FO AND MYSELF) DISCUSSED UPCOMING FLT. THE LAST THINGS DISCUSSED WERE RWYS IN USE AT BOS. DEPARTING RWY 9; ARRIVING 4R; WE WERE CLRED TO RWY 9 VIA 'OUTER SIERRA; HOLD SHORT RWY 4L.' THE YELLOW SIGNS BTWN THE S OUTER AND INNER TXWYS WERE UNLIT AND AS A RESULT WE WOUND UP ON E1; CROSSED RWY 4L; JOINED SIERRA TO RWY 9 (RWY 4L WAS NOT IN USE AT THIS TIME) AS WE APCHED RWY 9/27. IT WAS THEN I REALIZED WE WERE TO HOLD SHORT OF RWY 4L NOT RWY 4R AS I THOUGHT I HAD HEARD. I'M SURE THE PRIMARY REASON FOR MY THINKING RWY 4R RATHER THAN RWY 4L WAS OUR PRIOR DISCUSSION OF RWYS IN USE. I ALSO EXPECTED TO SEE LIT 'INNER;' 'OUTER' SIGNS TO DENOTE THE L TURN ON THE OUTER AND INNER TXWYS. I REALIZE THIS PARTICULAR TAXI RTE (S OUTER) ISN'T VERY HEAVILY USED BUT I THINK LIGHTING THE AFOREMENTIONED 'INNER' AND 'OUTER' SIGNS WOULD BE AN AID IN AVOIDING ANOTHER SUCH OCCURRENCE. ALSO; THE RED RWY 4L/22R SIGN DEFINITELY FAVORS TFC ON TXWYS E AND S. A SIMILAR SIGN ON THE R EDGE OF TXWY E1 WOULD BE ANOTHER REMINDER TO CREWS SOMEWHAT UNFAMILIAR WITH BOS THAT THEY ARE APCHING A RWY.