During the transformation of the existing social Web to semantic social Web, semantics-enriched social computing is becoming important, because it can support semantics-oriented user connection and collaboration in a larger community. To provide this support, this paper proposes a novel sign-based social computing approach, called Sign Network, to represent and exchange semantically intero-perable Web content between online computer systems. This approach semantically enriches social content and enables to mediate the communication of Social Web users such that their social content can be unambiguously created and used. Applying this approach, a social sign exchange mechanism is developed for enabling the applications of social tagging, social navigation and social collaboration.