@loops I've also used it and seen it used by the disabled and autistic communities for alignment around, e.g., #BoycottToSiri, #CripTheVote, #puppetgate, etc (which Dr. Flowers mentions). It was a relatively common way of engaging in conversations like #autchat on twitter as well.

I am talking here on the use cases that I have experience with and used, but I've seen it used in Black communities exactly as @shengokai describes it as well: for call response, etc.