It indicates the car speed.
See also:
Folding Mirrors
The exterior mirrors are hinged to allow the mirror to pivot forward or rearward
to help avoid damage. The mirror has three detent positions: full forward, normal
and full rearward. ...
Air bag failure
Turning the ignition key to MAR the warning light on the dial turns on, but it
should go off after few seconds. The warning light stays on glowing steadily (on
certain versions together with t ...