In this paper, the second of three in a series, I define what I mean by semiotic systems, using examples both from the teaching and learning of mathematics and from research mathematics. After locating semiotic systems within their ever-present social contexts of use, I go on to explore more broadly the semiotics of mathematical text. Using the social semiotics of Michael Halliday, I delineate three metafunctions that can usefully be applied to mathematical text. These are the ideational, interpersonal and textual function. I explore the first of these, the ideational textual function, in this paper. The remaining two functions are discussed in the third and final paper in the series.