Highway departments place signs by the roadside in order to clarify what happens just ahead. People depend on signs, especially when they are in area they are not familiar with.
Whenever there is a serious accident on our roads, some kind of investigation should be conducted. Police conduct their own investigations, and so do insurance companies. Since this is the case, it is wise to conduct your own, through an experienced attorney or private investigator.
As questions go, this one seems pretty obvious. Of course you know what an injury is. It's a broken arm, or a laceration, or a truck running over your foot. Something bad and obvious that happened to you.