PIPER PLT CONFUSES CLRNC AND FINDS HIMSELF ON THE DEP END OF THE RWY BEING USED FOR DEP.

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I CALLED FOR MY IFR CLRNC AND TAXI CLRNC. I WAS GIVEN BOTH; CLRED TO TAXI TO RWY 18. I TAXIED OUT; AND DISCOVERED I WAS ON THE DEP END OF RWY 18. I CALLED GND AND TOLD THEM WHAT I HAD DONE; AND THEY CLRED ME TO BACK TAXI AND CALL FOR MY TKOF CLRNC WHEN READY. AS AN ACR PLT; I ALWAYS HAVE MY ARPT DIAGRAM OPEN AND REFER TO IT CONSTANTLY WHEN TAXIING; AND ASKING FOR HELP IF I NEED IT. I WAS DOING THIS AT JOPLIN ON THE DAY UNDER DISCUSSION; PARTICULARLY SO BECAUSE THERE IS SOMETHING ABOUT THE WAY JOPLIN ARPT IS LAID OUT THAT DISORIENTS ME; EVEN THOUGH I'VE BEEN THERE NUMBERLESS TIMES. I KNOW A LOT OF TIME AND MONEY HAS BEEN SPENT TO DEVELOP A SYS OF SIGNAGE AND SURFACE MARKINGS; BUT I THINK I WAS LED INTO A TRAP BY THE RWY SIGN WHICH; EVEN THOUGH IT IS RED (AND SOMEHOW THE COLOR DIDN'T REGISTER ON ME); IT SHOWS AN ARROW POINTING STRAIGHT AHEAD. INTUITIVELY; THIS INDICATES 'RWY THIS WAY;' WHICH IS WHERE I WENT; RIGHT ONTO THE RWY; THINKING I WAS BEING DIRECTED BY THE SIGN TO THE RWY VIA A TXWY. I SHOULD HAVE BEEN LOOKING MORE CLOSELY AT MY TXWY CHART; AND IT SHOULD HAVE DAWNED ON ME THAT RED MEANS STOP. I'VE BEEN THINKING ABOUT THIS INCIDENT THE LAST COUPLE OF DAYS; AND THE ONLY THING I CAN THINK OF TO KEEP THIS FROM HAPPENING AGAIN IS JUST TO REDOUBLE MY EFFORTS TO PAY CLOSE ATTN TO MY TXWY CHARTS; AND BE AWARE THAT IT IS POSSIBLE TO MAKE A MISTAKE; EVEN THOUGH I'VE NEVER MADE THIS PARTICULAR ONE BEFORE. ALSO; IT MIGHT BE A GOOD IDEA TO REVIEW THIS TYPE OF SIGN. I THINK THAT IF THE SIGN HAD JUST BEEN '18;' (RED WITH NO ARROW); I THINK I PROBABLY WOULD HAVE STOPPED.