I did say "pavement markings or signs", and this was meant to cover both types: here in California, a "trail" can refer to anything from a minimally-improved dirt route through the forest no wider than a person, to an asphalt-paved multi-use facility with smaller versions of the familiar traffic control signs.

In the context of OP's question, I didn't specifically discuss narrow, single-track trails because there's no possibility of a bicyclist squeezing past a pedestrian without it being a very obvious negotiation of space.

But there are plenty of regional trails which reuse the alignment of an old fire road or railroad. So the prospect of riding a bicycle on dirt in a 3-meter wide dirt corridor is not unheard of. So to come across a pedestrian is also not abnormal. If the weather is good, all walks [no pun intended] of life will make their way to enjoy the outdoors here.

Regional recreation areas will post their trail rules at the trailhead, and periodically along the trails. Some rules are obvious, like not littering. Others are not: horses sometimes get priority over both cyclists and pedestrians, because in areas with lots of horse riding, the horses could get spooked and bolt.