My local police force figured out that bikes, being so stealable, made an excellent entree into the world of stolen property. They rigged up a bike with a radio beacon, left it chained with a weak lock, and just waited a few hours for it to get stolen. They tracked it to a lock up garage which was full of stolen property from burglaries etc, and were able to solve a whole lot of crimes in one swoop.
Bike muggings are a different matter, the most important thing is to avoid serious injury, bikes can be replaced. Mark your bike with a permanent stamp, under the bottom bracket, with your zip code. Put a tag with your zip code inside your seatpost and handlebars or stem, so the next guy to repair it knows that it is stolen.
If gangs are a problem, use your mobility to keep some distance, and stay observant. Learn how to ID someone, estimate their height and weight, how to note down significant ID features such as tatoos or scars, hairline, nose shape etc. Clothes can be easily changed, but shoes and watches are not changed every day.