The aim of the present work is to discuss a limited set of issues which concern the grammar modelling of Greek Sign Language (GSL) within the framework of improving the naturalness and more specifically the grammaticality of synthetic GSL signing. This preliminary study addresses the linguistic issues relating to specific grammar structures and their related prosodic expressive markers through experimental implementation of the respective rules within a sign synthesis support environment that was initially developed in order to create lexical resources for GSL synthesis.