You can't know it is a weapon. It is on your back. I've never been handcuffed, but they can hurt.
I have, however, been surrounded by cops taking folks home. Some friends of the dude I was dating, and we happen to have different skin colors. 4-5 cop cars, lights, drug dogs in a small public housing parking lot. I start getting questioned about drugs, and expected me to know a lot about my passengers. "People have been doing crack here, and we've found out white people are doing it too". I was let go, and to this day I hope those dudes were ok.
I've been pulled over for swerving after a lane change. Dude said we were drunk, even after we passed the breath test. It was late, we were driving around talking, but happened to be in a mostly poor, african-american part of town and we weren't. Her baby was mixed, though. It worked, we called it a night simply because of harassment.
Had guns out once with lots of cops. I'm still not sure what I did wrong. The park closed at 11, but since it was getting dark a parks department employee asked us to leave (but not the other people). Down the road we were surrounded, guns out.
The point is that there are a LOT of these sorts of stories, and it has taken a few killing with news coverage for them to finally - 20, 30, 40 years later - for anyone to start doing anything about them.
I was lucky enough to get out of my fear of the police because I've since moved. Racism exists everywhere, but not everywhere will tolerate it from their police department. When I'm out walking home at 2am here, I'm no longer afraid of the police. I won't even get stopped asking what I'm doing out, why i'm in a neighborhood, etc. So long as I'm just walking along, everything is good... and i'm in a city of 180k people.