Metacognition relies on representations, which are commonly viewed as internal knowledge structures. We explore the idea that external embodied diagrams, rather than monomodal symbolic-based entities, can provide an accurate description of metacognition in choreographic dance. When marking, dancers use their bodies to represent properties, dynamics, or structures of dance phrases. Marking-for-self occurs when a dancer marks the dance in their own unique manner, potentially allowing for real-time reflection through the manipulation of external signs. These manipulations can be considered diagrammatic semiosis, as diagrams signify shared relational parts analogous to the parts of their objects. Based on Peirce’s semiotics, we argue that semiosis is crucial for metacognition. This paper is structured to first review marking and marking-for-self, followed by an overview of metacognition. We then define marking-for-self as a metacognitive phenomenon and introduce Peirce’s concept of semiosis and diagrams. Finally, we describe marking as a diagrammatic sign and explain how marking-for-self is an embodied metacognitive process achieved through the manipulation of diagrammatic structures.