The sign above says "No foam boxes used" and was shown at a restaurant in Nan town. And I like this because food take-away in these foam boxes is really terrible. These boxes are very bad for the environment and are said also to be unhealthy for using them for food. So many restaurants will put a plastic cover under the food. But in Thailand the use of single-use plastic is a environmental disaster. You get plastic bags, etc. almost everywhere.
So when you are traveling in Thailand please say no when people give you a plastic bag, foam box, a plastic spoon or a straw to drink. In many cases you can actually avoid using them.