zdnet[.]com/article/that-antifa-terrorist-label-you-saw-on-threads-and-reddit-its-not-what-you-think/
I don't know how many use Threads, but Reddit can be hard to avoid if you Google most anything.
The label says:
In italics below the content of a post, you might see a warning label seemingly added after the fact that says: "This user is suspected to be a part of a terrorist organization called Antifa. Please report any suspicious behavior."
That could be confusing, so a quick explainer of sorts... the US is currently politically divided. There's an ideology that some on the left subscribe to by varying degrees -- the movement, if you can call it that, is named Antifa, as in anti-fascist. There is no formal organization. Many on the political right however use Antifa as a broad label for people they believe are left wing extremists, treating Antifa as an actual organization of some sort. US President Trump recently officially designated Antifa as a terrorist group. That's led to mocking from the left since there is no real group or organization, and the labels are part of that mocking.
The text is being added by the users themselves on everything from posts to memes to recipes, and it's formatted to look different. Users are adding the tag to protest (or mock) President Donald J. Trump identifying Antifa as a domestic terrorist organization.
wikipedia[.]org/wiki/Antifa_(United_States)