I used to live in the neighborhood of the original Black Panthers. Nearby Santa Fe Elementary on 54th & Market St had several children struck by cars. The Panthers petitioned the city of Oakland to install a crosswalk, which they did not do. So the Panthers instituted a neighborhood crosswalk enforcement team, which helped children get to school consistently. Eventually, the city (recognizing the bad press of doing nothing) installed a crosswalk. There's also a historical marker sign commemorating the story but I couldn't find it on street view, so take my work for it or explore for yourself

EDIT: found it. 55th and Market, Street view, SW corner pole of intersection, a black and yellow sign at pedestrian-signal-height, right near the blue USPS box