I proposed light_smile a while ago (forum #46981) but intentionally leave out implication to smile. This tag is intended to cover expressions that are too gentle to be called a full smile (e.g. post #901540, post #904305, post #908375).
Basically if you see a very pleasant expression, but are hesitate to call it a smile, tag it light smile. Of course borderline cases can be tagged with both (e.g post #893620). So I wouldn't like an implication.