This paper explores an atypical grammaticalization process of a co-speech gesture to a functional sign which can be observed in many unrelated sign languages. In particular, we discuss the ‘palm-up’ gesture and a corresponding illocutionary gesture available in spoken Italian, the so-called ‘artichoke’, in more detail and show how these two gestures have developed in the respective sign languages to grammatical sentence-type markers. We argue that the pragmatic potential of these co-speech gestures described for many spoken languages paved the way for a syntactic integration as illocutionary force modifiers in spoken languages and subsequentially for the grammaticalization as sentence-type markers in sign languages. We claim that this modality-specific grammaticalization process follows general well described grammaticalization paths if we assume that gestures can be syntactically integrated and systematically associated with specific functional domains in the left periphery. While the grammaticalization of question particles in spoken languages is well documented in formal and cognitive linguistic theory, the corresponding syntactic integration of gestures in the functional domain has not yet been thoroughly investigated in formal linguistic theory.