I don't feel like I did this question justice with my previous answer.
The most obvious example would be the George Floyd video, and in a larger sense, the extremely effective tool of filming police as they harass, plant evidence on, beat, and murder the people they're supposed to serve. In the current situation, I think the results of that video speak for themselves.
In response to the pervasive narrative that focuses on looters and not on cops murdering black people (I linked to five minutes in, but the whole thing is worth a watch): https://www.youtube.com/watch?v=SWE8k5EUonE&t=5m0s This tends to be persuasive in my experience.
This doesn't address racism because it's a white guy, but I find it's effective in getting people to take the complete lack of police accountability more seriously: https://www.youtube.com/watch?v=VBUUx0jUKxc That officer (Philip Brailsford) was acquitted in a trial where the prosecutor moved to strike the video from evidence, and then the officer was rehired by Mesa Police briefly, before being given early medical retirement based on a claim of PTSD from the murder, earning him a $2500/mo pension.
Watch any of those videos that you haven't seen, and see how that feels, and realize that that's how they make people who were on the fence about these issues feel.
That second video is revolting. I don't think I can correctly articulate my thoughts after watching that.
Wow. Just wow.