Here is the answer: San Francisco gang members, the Divisadero Gang, all wear Palestinian kaffiyahs.
When told by teachers and administrators at their Gateway High School the connection between the kaffiyahs and terrorism they said they 'knew that... it is the reason they wear the kaffiyahs'. No gang colors, just a provocation for police and other people who know what the kaffiyahs symbolize. Nearly all the Divisadero gang members are black. They have killed several teenagers and wounded many more.
The good news: Jew-hating-kaffiyah-wearers who wander into the Western Addition of San Francisco will be attacked by gang members and are also likely to be attacked by rival Nortenos gang members in the Mission area too.