The Surfers Park Danger Sign is located in the top right portion of the map in big city area. Use
to show just the Danger Signs. You will need a lot of speed to achieve a 450 foot jump to get a three star rating. Start on the road leading up to the ramp and then turn towards the jump and avoid the trees. If you hit a tree just use the rewind. I had a hard time going off the jump without it making the car roll one way or the other. Try to hit the ramp dead center without steering at all. I had to hit the ramp at around 160mph to get enough distance. Good luck!
EDIT: Sounds like most people needed more speed than I posted. I got 453 feet and I left the ramp at 160mph. Here is a clip to hopefully help some people with the approach and the angle needed to get enough distance.
Thank you darkavenger786
for the clip!