Seeing a motorcycle in the mirror is worth two points
When you spot a motorcycle in the mirror, say out loud either "Motorcycle!" or "Motorbike!" - two points." Once a motorcycle is spotted no other player can receive points for spotting it. Only the Driver can get points by using the mirrors.
Since a Driver is at a disadvantage when playing against other players that are Passengers, they can make up their disadvantage by spotting with the mirrors.
If another player says "Motorcycle!" at the same time the Driver does, the driver is awarded the points.