I caught a clip from a tv show a few years back and I think it was Prime Suspect. I wanted to find out for sure so I could watch the whole thing.
All I can remember is a woman (or it may have been a girl) lying in a hospital bed trying to help police with their enquiries. She is badly injured and can't speak due to bandages etc but can only manage to draw.
She draws a jagged line on a piece of white paper which means nothing at first to the police, but then we see a flashback to a scene, shown as her memory of something that happened to her and the jagged line is what is drawn on the back of a white transit van - presumably one that was involved in the crime.