See also:

Heated mirrors (if so equipped)
Some outside mirrors can be heated to defrost, defog, or de-ice for improved visibility. For additional information, see “Rear window and outside mirror defroster switch” in the “Instruments ...

Troubleshooting guide
...

Removing spots
Remove tar and oil spots, industrial dust, insects, and tree sap as quickly as possible from the surface of the paint to avoid lasting damage or staining. Special cleaning products are available ...