Anarchism

Around here (Brazil), during manifestations, the police will search every bag they can see. While the clothes alone are obviously "nothing", I wouldn't be surprised if they came up with bullshit reasons to take you away or keep a very close eye on you, or if some damning evidence "magically" appeared.

Also in Brazil free speech is only protected if it's not anonymous.

Police and the fucking army abused that a lot during those times, btw. There are a number of videos of police detaining, then releasing specific black blocs, or being suspiciously non-violent. Not to mention the many times cops were caught planting evidence, one I recall seeing was with 3 cops searching a backpack, one of them turned it upside down to see if anything would fall out of it, meanwhile another cop stealthily dropped a bunch of fireworks and used that as proof to arrest the person.

I've actually been stopped by uniformed officers minutes after spotting the absolute most obvious undercover cop in the world in Ohio.

My crime? I said "Good Morning OFFICER!" really loud as I passed him at the park. There were a lot of people walking around for an art festival and supposedly the local PD got a "tip" it was being used to hide "illegal liberal activities"

Dude was wearing preshly pressed clothing that looks like he literally bought it from Abercrombie that morning. Basically the whole outfit says "I am trying to fit in, this is what we see you people as, look at how hip and cool I am fellow kids" and the haircut was so out of place I literally did a double take.

COPS don't know how to not be cops, even when they're trying their hardest to pretend so they can catch people doing mysterious and vague criminal things.

Very likely, but also very likely just common criminals.
If there were legitimate Black Blocs in those protests they were a minority.