Is it safe to reheat food in takeaway plastic containers? What about heating up food in a melamine bowl in the microwave?

I usually look out for the microwave safe label on the containers. If it is not stated, I will see what is the number within the "triangle" (the one made out of three arrows, and looks similar to the recycle symbol, all plastic containers should have that). If it is 5, it should be safe for use in the microwave. If I'm using bowls, I will use glass or ceramic ones for microwave.