Document your car's damage and the postion of the sign with photos. Get estimates for the repairs. Be sure to tell the repair place why you are doing this. Most good repair places will add 20-40% to the bill if you tell them its for a potential court case. Don't worry, they wont charge you the extra 20-40%. That is just the fudge factor because the contractor will probably offer you only 3/4 of the money needed to fix your car. Then find you who the contractor is and FedEx your proof to them with a threat if they don't pay to sue them. If they offer money, take it. If they don't, go to small claims court. It won't be a slam dunk to win the case, but hey, its better than doing nothing. Best of luck.