This paper approaches the gestural sign from a cognitive-semiotic perspective combining Peircean semiotics (Peirce, 1955, 1960) and conceptual metaphor theory (Gibbs, 1994; Johnson, 1987; Lakoff, 1993; Lakoff & Johnson, 1980, 1999; Müller, 2004; Sweetser, 1990). It suggests that these two theoretical strands share central assumptions regarding image-schematic structures, metaphorical projection, and habitual patterns of experience and interpretation (Danaher, 1998) and that exploring spontaneous co-speech gesture reveals additional points of cross-fertilization. In the gesture modality, embodied structures are re-externalized and visualized. The corpus for this study consists of videotaped academic discourse and gestures produced by four linguistics professors during introductory courses. Applying Peirce’s taxonomy to gestural representations of grammatical concepts and structures, the study demonstrates in what ways his categories of icon, index, symbol, and especially the less widely used sub-categories of iconicity (image, diagram, metaphor) allow to capture both fine distinctions between and transient cases of sign-object relations within a metaphorically accessed domain. Forms of interaction between iconic and indexical modes are also briefly discussed.