The Guardian Angels and their citizen “safety patrols” were born on the New York subway about 40 years ago in response to the city’s crime-ridden transport system.
More recently, a new division of the group has formed – a women-led group called Perv Busters which aims to prevent sexual assaults on the transport network.
The BBC Travel Show finds out more.
The New York Police Department advises that if you have been a victim of, or a witness to, any form of improper sexual conduct, you should immediately report it to law enforcement or an MTA employee. Do not try to handle it on your own.
The Travel Show can be seen on BBC World News.
If you have been affected by issues raised in this video help and support is available via the BBC Action Line.