SMA TAXIED ACROSS UNUSUAL HOLD LINE ON TXWY APPROX 1000' FROM DEP END OF RWY. ARPT MARKINGS NOT CLEAR.

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I WAS PILOTING A TRANSIENT ACFT THAT HAD ARRIVED EARLIER IN THE DAY. I FLEW IT IN AND LANDED ON RWY 21 AT CHO. I CALLED AND RECEIVED CLRNC FROM CHO GND TO TAXI TO RWY 21 FOR DEP. I TAXIED FROM THE RAMP ONTO THE TXWY AND PROCEEDED NEBND. I CAME UPON A RED SIGN WITH WHITE LETTERS OFF TO MY LEFT WHICH READ: '3-21;' AND SAW A YELLOW HOLD LINE ACROSS THE TXWY. THIS WAS JUST PRIOR TO AN INTXN ON THE LEFT (200' APPROX) MARKED 'E.' THERE WAS ALSO AN INTXN ON THE RIGHT (200-300') WHICH WENT INTO ANOTHER RAMP AREA. I WOULD ESTIMATE THIS SIGN AND HOLD LINE TO BE AT LEAST 1000' FROM THE THRESHOLD OF RWY 21. I CONTINUED TO TAXI TOWARD THE THRESHOLD OF RWY 21 WHEN THE GND CTLR INFORMED ME THAT I HAD CROSSED THE HOLD LINE FOR RWY 21 SOME 300' BACK. I STOPPED; TURNED AFTER RECEIVING A BACKTAXI CLRNC; AND STOPPED ON THE S SIDE OF THE HOLD LINE WHERE I DID MY RUNUP. I THEN CALLED THE TWR AND SUBSEQUENTLY DEPARTED FROM THE INTXN OF 'E' ON RWY 21. NOTHING FURTHER WAS SAID BY ATC CONCERNING THIS INCIDENT. I BELIEVE THERE WERE SEVERAL FACTORS AT WORK HERE WHICH LED ME TO CROSS A LINE WHICH I RECOGNIZED AS A HOLD LINE. BECAUSE OF THE PROX OF THE INTERSECTIONS ON BOTH THE LEFT AND RIGHT OF THE TXWY; WELL AHEAD OF MY POS; I BELIEVE I WAS NOWHERE NEAR WHERE ANY HOLD LINE FOR RWY 21 WOULD BE. SINCE I WAS AT LEAST 1000' FROM THE THRESHOLD; I DID NOT PROCESS THE SIGNIFICANCE OF THE LINE TO MY INTENDED OPERATION ON RWY 21. CLEARLY TO ME; I WAS NOT IN PROX TO THE RWY ENVIRONMENT FOR RWY 21. SECONDLY; THE SIGNIFICANCE OF A RED SIGN WAS UNKNOWN TO ME. I HAVE SINCE ASKED SEVERAL PLTS NONE OF WHOM KNEW THE RED SIGN WAS ASSOCIATED WITH A HOLD LINE. (AIM PARAGRAPH 60 HAS AN OBSCURE REF). THIRDLY; THE TYPE ACFT I WAS FLYING REGULARLY OPERATES FROM FIELDS ONLY TWICE AS LONG AS THE DISTANCE THAT REMAINED TO THE THRESHOLD. THUS; I PROBABLY FELT THAT I HAD A LONG WAY TO GO UNTIL I REACHED THE THRESHOLD AREA. FOURTH; THERE IS NO SIGN THAT CALLS ONE'S ATTN TO THIS UNIQUE SITUATION. THE NORMAL SIGNING IS IN PLACE; BUT ITS SIGNIFICANCE IS DIMINISHED BY ITS LOCATION AND ANGLE TO THE TXWY/RWY/INTXN. FIFTH; ATC GAVE NO CAUTION TO EXPECT THE IRREGULAR LOCATION OF THE HOLD LINE. SIXTH; I HAVE OPERATED AT CHO BEFORE AND DO NOT REMEMBER HAVING COME ACROSS THIS SIGN OR SITUATION. IT HAS BEEN A FEW MONTHS THOUGH. I RECOMMEND THAT A SUPPLEMENTAL SIGN BE INSTALLED WHICH WILL CLEARLY INDICATE THAT ACFT SHOULD SWITCH TO THE TWR FREQ AND NOT PROCEED BEYOND THAT POINT WITHOUT ATC AUTHORIZATION. I SUSPECT THIS HAPPENS OFTEN AT CHO; AND IS IN NEED OF A REMEDY. CIRCUMSTANCES WHICH ARE SO GROSSLY NONSTANDARD WILL OFTEN BE IGNORED; SUCH AS PUTTING A RED LIGHT IN THE MIDDLE OF THE BLOCK WHERE NO INTXN EXISTS.