Mathematics is a highly specialised arena of human endeavour, one in which complex notations are invented and are subjected to complex and involved manipulations in the course of everyday work. What part do these writing practices play in mathematical communication, and how can we understand their use in the mathematical world in relation to theories of communication and cognition? To answer this, I examine in detail an excerpt from a research meeting in which communicative board-writing practices can be observed, and attempt to explain the observed exchanges with reference to relevance theory (a cognitivist theory of linguistic pragmatics), in combination with the situated cognition paradigm (which considers how physical and social contexts are involved in thought itself).