Okay this achievement is annoying and whilst the guide made by vXTotalChaosXv is perfectly fine it did not help when it came to what build he used to get the job done. So I am adding my own input and clip of it succeeding just to help anyone who isn't too sure on how to approach it. Now I live in the UK so to get 3 stars on the Surfers Park Danger sign I needed to hit a minimum of 137 metres. Yes it does it in metres and I ain't switching to feet.
Now the most important part is getting a nice clean run up without really slowing down at all, to do this abuse the rewind button over and over until your satisfied with the run up. And then simply aim pretty much for the dead centre of the sign. I hit the sign at around 172MPH and maintained a good 150+ whilst in the air. So try and aim for these numbers and avoid that bloody tree.
And the main reason for making my own solution is in this part, now for the build I used for the car. I upgraded to Race Brakes. Added the Offroad Springs and Dampers. And changed my car to the offroad tyres, this was so all because most of this sign requires you to drive ridiculously fast on the grass.
Video below of it getting the job done this took a good few attempts and sadly the video does not show the achievement popping just because that is how the Xbox recording software seems to work but trust me it got the job done and beat my personal best!