Sadly, the only thing you can do is to report your suspicion. However, they’re not likely to take any action unless an actually crime has been committed. But you could never control those gangs. And if you’re scared that maybe things would get more worse, well you could try getting pepper sprays, pocket knives or tasers and carry them with you as a self defense weapon. Also try learning self defense if there’s more time. If you feel you don’t want to report it, try knowing what the gang want. Try negotiating. Try finding alternatives for what they wanted if you can’t give it. Never lose guard. Be safe.