Sorry, yes UK. I have the impression that Duolingo is predominantly based in/on USA and Lat Am usage, viz almost complete absence of vosotros forms. I guess that's why I didn't qualify my "we". In the UK the police often put "Police Aware!" stickers on crashed or abandonned cars, to save being rung up by everybody. "Known to" and "known by" don't seem to be predictable from "por". "Known by"is not unusual in UK.