Some semi-interesting follow up information for those who encounter a no-heat situation in their mirrors. If you have the lighted switch/timer on the dash showing the rear window and mirrors, then your car has (had) the heated mirror feature. (Answer to original question.)
The mirror heater element is glued onto the back of the mirror, which in turn is glued/industrial strength taped inside the mirror mounting plate. Forget about fixing just the mirror heating element, which should probably show around 7 ohms if it is good, and much higher resistance or open when bad. Everyone know how to use a meter? Seven Ohms!
You can replace just the mirror glass, which can be purchased aftermarket, IF you are lucky and have removed the mirror/mounting plate assembly from the mirror housing without snapping the plastic locking tabs off the plate. It isn't that easy. Those who can do it have wrecked lots of them learning how. Then there is the job of removing the old glass from the mounting plate and re-gluing the new glass. Personally, I would rather be sitting in an air-conditioned room drinking beer.
Aftermarket heating strips are available, if you've progressed that far without breaking stuff, but this is a fabrication step. Besides, mirrors go through a lot each winter with rain and snow covering the internal motors, heater and wiring. If you are having fun, be sure you know which type of mirror assembly you have before reaching in and pulling! Or, if you really want some entertainment, buy someone else's mirrors that have already failed!
Fortunately you can purchase a set of heated mirror assemblies (the complete thing!) for about $125 and save yourself a lot of trouble and hair loss. Plus you can replace the 4 front window regulators at the same time, which are almost certainly ready to fail.
So, yes, my own 940 did have heated mirrors. Both died at some point and I'm sure there are lots of them out there. Good Luck!
Lazarus