General aviation pilot reported a runway incursion when the pilot taxied past the assigned taxiway hold point and a landing aircraft was instructed to go around by ATC.

Narrative

Runway at SGJ is 13/31. Traffic was departing from 31 on Day 0. Received Ground instructions to taxi and hold at B6; which is last taxiway prior to 31. Received subsequent instructions to hold at Runway 31 and switch to Tower. NOTAM for airport lists 'runway markings faded'. Pilot mistook the instructions to 'hold at 31' and misinterpreted lines between Taxiway B6 and Runway 31; and proceeded past hold for Taxiway B6 (which is also the hold for Runway 31) to edge of Runway 31. After switching to Tower; Tower informed pilot that he had proceeded too close to runway without permission and approaching aircraft went around. Proximity of aircraft was not within about 500 linear feet; but was technically a runway incursion although aircraft was not on Runway 31. The runway markings; instructions; and taxiway positions for entering Runway 31 at SGJ are confusing without local knowledge and the NOTAM added to the confusion. Suggest that SGJ Ground replace 'hold at Runway 31 and switch to Tower' to 'hold at B6 and switch to Tower' to avoid confusion in the future for Runway 31.