@Shufei Earlier in the year I was biking around my city and ran into a randomly heavy police and homeland security presence loitering downtown. Shortly after that I pass a small anti-police protest by the local DSA, being sandwiched by the above.
I found out this protest was apparently a) unregistered with the city (to make it a "surprise action")... and b) planned entirely on facebook. I discovered those facts because I googled some of the details (date, city, "anti-police protest") and got a link to their fb group page as a top result.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko