On weekday mornings, San Francisco residents, mostly in their 20s and 30s, many in jeans and hoodies, a few in khakis and tucked-in dress shirts, form a single-file line against a mural-graced wall by the Muni bus stop at the southeast corner of 24th and Valencia streets. They know each other well enough to line up following a system that lacks public signage, but rarely engage in conversation. Here they wait to catch a ride…