This hashtag is usually used on posts which feature a link to an "Anonymous video". Anonymous videos are often hosted on YouTube, although they could be hosted anywhere, and they typically feature a synthesized voice reading a manuscript which was written by any old nobody.
There are, however, many different faces to Anonymous, and a video can take many different forms, but if it claims to be "Anonymous" then it is, by definition, "Anonymous".
As always, no one can speak for Anonymous. Anonymous speaks for itself. So whatever an Anonymous video contains can never represent the whole of Anonymous. Anonymous is Everyone, after all. So take everything with a grain of salt, use your critical thinking skills, and cross-reference any information that is delivered "as fact" wherever possible. (And never stop developing those critical thinking skills. It's something we can always get better at.)
It's also a good idea to consider the emotional impact of an Anonymous video before sharing it on Openbook. A good Anonymous video inspires one toward taking thoughtful, constructive action for the good of all people. It inspires you to feel a part of a faceless collective that includes all of humanity, all working toward a better world for all, and working against the divide and conquer agendas of the dark forces. On the other hand, an Anonymous video which fills you with fear, and doubt, and causes you to shut down, may not be worth posting here on ~camp.