The sign for "microwave" is very similar to signs based on the concept of "light." The "microwave" sign basically shows the microwaves being broadcast from the sides into the food in the middle.
MICROWAVE:



MICROWAVE (version):

MICROWAVE (3-digit version):
MICROWAVE (3-digit version 01):
MICROWAVE (3-digit version 02):
Sample sentence: "Do you prefer to use the stove or a microwave?"
= YOU FAVORITE STOVE [bodyshift] MICROWAVE, WHICH?
Notes:
Some people just spell "MW."
A cute joke sign I've seen for the sign "microwave" is to "wave" the tip of your pinkie up and down by flexing it at the smaller two knuckles. Geddit? A "micro" wave. (Ahem.)
Notes:
See: FOOD
See: COOK
See: BAKE
See: WARM
See: HEATSee: OVEN
See: STOVE
Notes: