General aviation pilot reported the lack of signage for a merged taxiway and unfamiliarity with the airport led to taxiing past the runway hold short line without clearance.

Narrative

While departing AGC from the west ramp FBO; my notes indicate I received taxi instructions: Taxi to Runway 31 via A; B; utilizing D; E on exiting ramp." This phrasing was slightly more complex than a simple sequential order. Ground offered progressive taxi; which I did not take advantage of.I used D and E to exit the ramp and joined A. As I continued on A; I was looking for the turn to B but never saw signage indicating the merge point. I later realized A transitions directly into B at this location. Believing I had not yet reached B; I inadvertently taxied past the Runway 31 hold short line without clearance; but did not taxi onto the runway itself. I recognized the error immediately; stopped; and the controller transmitted nearly simultaneous to my stop.Tower instructed me to taxi briefly onto Runway 31; exit at B1; and continue along B to the correct hold short. No other traffic was present.Contributing factors included unfamiliar airport layout and signage at the A/B transition. I had also not utilized the offer of progressive taxi at an unfamiliar airport; and was further distracted from resolving a transponder and GPS reset issue prior to taxi while parked. High cockpit heat also increased felt workload.In the future; I will accept progressive taxi when offered at unfamiliar airports; be alert for similarly merged taxiways; and confirm position on the diagram via GPS when possible."