What do the symbols on my freezer mean?

I have a miele freezer, the size of a small fridge, and it has three lights on it, in order they are: yellow, red & green. There's an "s" and a triangle, I want to understand what all these mean. I can't find a make or model number on it anywhere, or other helpful information - I bought it second hand - and it works fine, but it has a lot of frost buildup, and once emptied, it builds up too quickly. I've checked the seal on the door, it seems fine. I'd like to alleviate this quick frost buildup.

Thanks!!