Don't confuse the criminal (including tickets and other violations) and civil legal systems--you can be cleared of any criminal charges, but still be held accountable to pay for the damage you did. Regardless of what happened with the summons and your ticket, the road commission can look to you to pay for the damage to the sign. You are not liable simply because you hit it--you would be liable, or financially obligated to pay, if you were at fault in hitting it. You would be at fault if you hit it deliberately, or--much more commonly--if you were driving negligently, or carelessly (e.g. texting or talking on cell phone; driving too fast; ignored a stop sign or light; etc.). If you do not feel you were at fault, you can refuse to pay; the commission would then have to sue you to force you to pay, and you could defend yourself by presenting evidence that you were not at fault.