"on the mirror" is correct and usable in written English.
You can use it to describe the location of something. For example, "The child drew a heart on the mirror."
When the light is turned on, the mirror helps to spread the light further and brighten the otherwise dull room.
This is the one I hang on the mirror of my dresser so I see it every morning.
He wrote 'Jewish-American Princess' in lipstick on the mirror".
(Infrared film on the mirror ensures that birds can see it).
Drivers can also summon emergency services by pressing a red button on the mirror.
On the mirror above the sink in the men's room it says, "WASHISTOPURGEISTODENYIS-TOWASHIS".
I check my teeth as I mouth the fancy French script on the mirror.
A sign on the mirror said the banana split were Special, fifteen cents.
One small bird flew into our roofless bathroom and danced on the mirror frame.
"The fix is that you put a window shade on the mirror.
More than 800 people have signed a petition calling on the Mirror group to reinstate him.
