Look at their boots. The cops wear their work boots while being Agent Provocateur(AP)
If you have old digital cameras with no GPS ability then take those for photos but don't take pictures of faces in case the camera gets taken away by the police.
If there is a violent protester, they will want others to join in but instead isolate them. I proposed in another post that if everyone as a group sits down it leaves the AP standing but that wouldn't work if you are marching. Maybe an idea would be to people to lock arms in a circle around the AP and push them out of the group, like white blood cells wrapping around a splinter to push it out.