>When I lived in San Francisco, backpacks were marginalized as being associated with being too poor to own a car. High-school students might carry a backpack, college students might carry a backpack, people on the bus might carry a backpack, but mostly not professionals who drove to work.
Huh? By extension you seem to be implying anyone who doesn't drive to work is not a "professional", which is bananas.
Smart people took Caltrain, BART, or a company sponsored gentrification shuttle into work and reclaimed the time they'd spend driving to "work". (AKA shitpost -- I noticed a remarkable uptick in trolling during commute hours back in the days I lived in the bay during rush hour.)
Anyways, no, carrying a backpack is not a sign someone is "poor" in SF, or anywhere else -- it's usually a sign they value their back.
Some folks wear messenger bags instead, but those were usually bicyclists.