I saw this on Feministing, and thought it was pretty interesting. This domestic violence awareness campaign from London puts a specific emphasis on the responsibility of those who might hear or witness this type of violence to call 911 (or 999 in England) for someone who might not be able to.

They also use an interactive video to convey this message -- depending on if you "choose" (by clicking) to call the police or not, you will get a different ending to the video.

Trigger warning.