Based on my very limited experience and the posts above, I'd say sign languages don't really have the luxury of having many "synonyms" with slightly different connotations, at least in the same way you'd list words in a dictionary. jbergstroem mentions "always trying to find the simplest way of explaining yourself", so I think the idea is people just say things how they are, in simple terms. I imagine ideas like politeness are instead conveyed in other body language, facial expressions maybe, instead of dancing with words.

But I'm just speculating, I'd love to hear someone's firsthand experiences here.