AN EXPERIENCED; BUT LOW IN TIME IN TYPE; C402 AIR TAXI PLT IMPROPERLY LINED UP ON RWY 31C AT MDW. AS HE PROCEEDED ON THE TKOF ROLL; HIS R PROP STRUCK A TXWY SIGN.

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AFTER TAXIING VIA TXWYS Y; K; AND F; I TAXIED ONTO RWY 31C AT MDW. I LINED UP ON WHAT APPEARED TO BE A RWY CTRLINE; AND APPLIED TKOF PWR. AFTER TRAVELING APPROX 400-600 FT; I STRUCK A TXWY SIGN WITH THE R PROP. AFTER ABORTING THE TKOF; I TAXIED BACK TO PARKING VIA TXWY Y. AS I TAXIED ONTO THE RWY; I WATCHED PRIOR LNDG TFC CLR THE RWY. I FOLLOWED THE TAXI LINE TO A LARGE WHITE LINE (I LATER DISCOVERED IT WAS THE LINE INDICATING THE R OF THE RWY). I BEGAN TO APPLY TKOF PWR IN STAGES. I HAD APPROX 20 INCHES OF MANIFOLD PRESSURE AND 2000-2200 FPM WHEN I STRUCK THE SIGN. I SAW THE SIGN ABOUT 1/2 - 1 SECOND BEFORE IMPACT. AT FIRST I THOUGHT IT WAS A CARDBOARD BOX (FROM MY POS IT AS ENTIRELY BLOCKED) AND THE IMPACT FELT NO MORE SUBSTANTIAL THAN THAT. HOWEVER; I CHOSE TO ABORT THE TKOF WHEN I HEARD AN ODD BUZZ AS I BEGAN TO REAPPLY PWR. I ALSO DISCOVERED THAT THE TAXI LINE CROSSES RWY 31C BUT DOES NOT CROSS RWY 13C. I FOUND THIS TO BE MISLEADING. IT IS VERY HARD TO IDENT RWY ALIGNMENT ON THE GND WITHOUT VERY CLR PAVEMENT MARKINGS BECAUSE THERE ARE SO MANY RWY AND TXWY LIGHTS AS TO BE CONFUSING. I FOUND OUT THAT I AM #4 OF 5 TO DO THIS.