Continuity mistake: When the Wraith first shows at the drive in, Packard's car hood shows signs of the gunshots that the Wraith blows in his car, but that doesn't happen until a few minutes later in the film. (00:28:00)
Continuity mistake: During the chase scene where they attach the "engine killer" remote to the Dodge M4S (aka Wraith's vehicle), 2 Chevy Malibu Cop cars are barreling up the road towards the racers. Once the cops pass the starting line, the cars are now Dodge cop cars. (00:44:25)
Chosen answer: I believe they are markers to show how many people are left to take revenge on for his death.
EMTurbo
The problem with that answer is that the Wraith had to kill five people (Oggie, Minty, Skank, Gutterboy and Packard) and he only had four of those metal braces. If he had one for each gang member he wanted revenge on, he would have had five. I think he was only given four chances to crash his car and reassemble, and once they were gone, that was it. That's why he killed Skank and Gutterboy at the same time.