Coordination between multiple autonomous agents is a major issue for open multi-agent systems. This paper proposes the notion of Behavioural Implicit Communication (BIC) originally devised in human and animal societies as a new and critical coordination mechanism also for artificial agents. BIC is a parasitical form of communication that exploits both some environmental properties and the agents' capacity to interpret their actions. In this paper we abstract from the agents' architecture to focus on the interaction mediated by the environment. Observability of the environment – and in particular of agents' actions – is crucial for implementing BIC-based form of coordination in artificial societies. Accordingly in this paper we introduce an abstract model of environment providing services to enhance observation power of agents, enabling BIC and other form of observation-based coordination. Also, we describe a typology of environments and examples of observation based coordination with and without implicit communication.