WHILE TAXIING ONTO RWY 10R AT SFO; B767 FLT CREW TAXIS ONTO UNSTRESSED HARD SURFACE BETWEEN TXWY S1 AND R.

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IT WAS OVERCAST AND THE TXWYS WERE WET. OUR TAXI INSTRUCTIONS WERE TO TAXI RWY 10R VIA TXWYS A; E; B AND HOLD SHORT RWY 10R AT U. WE ASKED FOR FULL LENGTH AND WE WERE TOLD HOLD SHORT RWY 10R AT S1. APPROACHING S1 WE SAW ALL SORTS OF SIGNS FOR TXWY WITH ARROWS IN ALL KINDS OF CONFUSING DIRECTIONS. BEING NIGHT AND WET MADE THINGS EVEN MORE CONFUSING. I WAS HOLDING SHORT AT RWY 10R AND S-1 JUST OUTSIDE THE CATII HOLD LINE. AT THAT POINT R; B; U; S1; AND S TXWYS ALL INTERSECTED INTO ONE BIG TARMAC TXWY WITH ARROWS GOING EVERYWHERE. WHEN I WAS CLRED ON THE RWY 10R; I TAXIED SOMEWHERE BETWEEN S1 AND R TO GET ON THE RWY. THE TWR SAID THAT WAS NOT A TXWY; BUT TO TAXI AT MY OWN RISK. I COULD NOT TURN AROUND AND AN UNEVENTFUL TAKEOFF WAS MADE. THE CONFUSION WAS THE CONVOLUTED TAXI SIGNAGE AT THE APCH AND OF RWY 10R; AND WITH ALL THE TARMAC; A PLT (AT NIGHT AND WET) COULD EASILY CONFUSE 'R WITH S1.' THEY FUSE TOGETHER. I DO NOT RECALL SEEING ANY BLUE TXWY LIGHT THAT DELINEATED TXWYS R AND S1 AND DIFFERENTIATED THE TWO. IT WAS DARK; WET AND CONFUSING; AND I FEEL THAT BETTER SIGNAGE AND TAXI LIGHTS WOULD HELP THAT THE PARTICULAR SECTION OF TXWY MEETING RWY AT SFO.