All police vehicles have flat mirrors. While the curved surface of convex mirrors causes cars and other objects to appear smaller and farther away, flat mirrors provide a true image which reduces the likelihood of misjudging the distance of objects.
Always adjust the rear view mirrors to clearly reflect the area behind the motorcycle before riding.
Adjust mirrors so you can see a small portion of your shoulders in each mirror. This will help you establish the relative distance of vehicles to the rear of your motorcycle.