If the plate you have is microwave safe the plate will usually say on the bottom of it if it's microwave safe.
However if it doesn't then most times the plate will be microwave safe.
For example, ceramic plates, plastic plates and glass plates are all really microwave safe.
I've microwaved food on ceramic and plastic plates without problems and I've put ceramic mugs in the microwave to heat up hot chocolate and coffee or tea before.
Most times the dishes you buy today are indeed all microwave safe.
As long as the plate or dish has no metallic edges or finishes they are microwave safe.
Even Styrofoam cups are microwave safe as long as you do not leave them in the microwave too long.