We survey recent developments in the formal semantics of sign languages, with four foci: (i) potential (and debated) cases of 'Logical Visibility', in which sign might make overt some logico-grammatical categories that are usually covert in speech; (ii) the pervasive role of iconicity; (iii) the comparison between sign with iconicity and speech with gestures, and (iv) the existence of universal properties of the signed modality.