Awarenesss (by potential victims as well as bystanders), self-protection, and personal responsibility (again, by potential victims and bystanders), are the best weapons against crime. Including rape.
If you see something, you can 1. Say something to a law enforcement officer, or 2. Act on behalf of the victim. This doesn't mean vigilante justice, or helping people who don't need it or aren't asking for help, but simply being human and treating others how you would like to be treated.
If someone is being taken advantage of, in any way, and you can help, why not help? You can't always live with the mindset that "someone will do something". If you are in a position to help, safely, that someone is you!
I'm just noticing now that I didn't add this before. Great post! @tarazkp