A C172 PLT; TAXIING FOR TKOF AT MCN; TAXIED PAST A HOLD SHORT LINE.

Narrative

I WAS TAXIING OUT FOR A VFR DEP AND WAS CLRED TO TAXI TO RWY 23. I HAD JUST ARRIVED EARLIER IN THE DAY; LANDED ON RWY 23 AND REMEMBERED XING THE APCH END OF RWY 13 WHILE TAXIING IN. I HAD A SMALL ARPT DIAGRAM ON MY KNEE BOARD (FROM AN AVIATION WEB SITE). I WAS TAXIING FROM THE MAIN RAMP AREA AND DID NOT SEE A RED AND WHITE SIGN TELLING ME WHAT RWY I WAS COMING UP ON. I STOPPED AT THE HOLD SHORT LINE AND COULD SEE A '3' ON MY SIDE BUT THE NUMBER ON THE OTHER SIDE LOOKED TOO NARROW TO BE A '2.' I LOOKED AT MY DIRECTIONAL GYRO AND THE RWY DID NOT APPEAR THAT IT WAS IN THE RIGHT DIRECTION TO BE RWY 23; SO I THOUGHT I WAS COMING UP ON RWY 13 AGAIN. AS I STARTED TO ROLL ACROSS THE LINE; I REMEMBERED THE TROUBLE I HAD WITH THE DIRECTIONAL GYRO PRECESSING ON THE LAST FLT AND LOOKED AT THE COMPASS. I IMMEDIATELY TURNED AROUND AND WENT BACK ACROSS THE HOLD SHORT LINE. I HAVE TAKEN AN AVIATION SAFETY PROGRAM AND ATTEND THE FREQUENT SAFETY SEMINARS. I JUST COMPLETED MY PROGRAM AND THE SEMINAR I ATTENDED WAS ON RWY INCURSION. I FEEL I DID NOT TAKE SUFFICIENT TIME BEFORE STARTING MY TAXI TO BE SURE I KNEW THE RTE TO THE RWY. CONTRIBUTING WAS THE ERROR IN THE DIRECTIONAL GYRO AND THE APPARENT LACK OF A SIGN (IT MAY BE THERE; BUT I DID NOT SEE IT) IDENTING THE RWY. NEXT TIME; IF I AM IN DOUBT AS TO MY POS; I WILL CALL GND AND ASK FOR CLARIFICATION.