> Since you don't know whose tracker it is maybe the best thing to do is "lose" it again.

Often, knowledge of surveillance almost completely diminishes its effectiveness. If you know your car has a tracker on it, the police won't get anything useful out of it, because you won't drive to any place you don't want the cops to know about.

Leaving it in place also has the advantage that you don't alert the police that you know about the surveillance.