Oh you mean this? What that cesspool aka Reddit won’t tell you, is that for less than US$20, you can get such vest and a helmet at hardware stores in Sham Shui Po. No credential required.
By donning a vest, you’re now a medic/doctor/aid-worker/journalist!
So, you can be one who happily throwing molotov cocktails but an hour ago, then decided to bolt when things doesn’t look that great for your team, you ditched that black t-shirt (some obviously too lazy to do that), put on a vest and pretend to be a medic!
And here comes the rub: this trick is getting so old after 6 months, the cops now simply arrest the whole lot.