Discription of Events: Passed our car from behind on a narrow, extremely windy road with an explicit "No Passing" sign. Visibility was also low at dusk because the area is very wooded and we were approaching the crest of a small hill. We were traveling at the speed limit so they were well above the speed limit as they passed, and as they drove away they flipped us off. Got a photo of them with the license plate in full view at the next red light.