Pilot reported confusion regarding red lines on the tarmac at BIH. The pilot was told they were 'restricted area' markings but they are not referenced in NOTAMs; charts; or safety publications.

Narrative

I departed ZZZ1 airport for a VFR flight to Bishop. After checking weather and NOTAMs; I had an uneventful flight and landed on [Runway] 30 at Bishop; exiting [Runway] 30 at [Taxiway] Foxtrot.I taxied over the ramp; past the pilot lounge; to the fuel island for self serve 100LL. As I taxied in front of the pilot lounge; I noticed red lines on the tarmac; and assumed them to be for the general public; not aircraft restrictions. There were no Airline aircraft at the terminal; the red area was empty. I taxied over the red lines.No pilot resource (NOTAMs; as well as airfield diagram and AFD remarks) mention the red lines or what they're for; and a sign would be useful. Being a small GA airport user; I have not come across these 'Red Restricted Area' taxi markings. A clear sign could have alerted me to taxi routing changes; maybe a quick note on the end of the AWOS message as well.I have since checked https://www.faa.gov/airports/runway_safety/publications/media/QuickReferenceGuideProof8.pdf; which doesn't define these red markings.