This study makes use of a reading of Prieto’s semiotics with the aim of shedding light on semiotic elements that occur during the discursive process in the classroom. Taking as reference an overview of this author’s theories in the context of science education, the paper focuses on the semiotic element of circumstantial indications. Circumstantial indications are a collateral and not always explicit type of sign in the teacher’s communication that assist the meaning of messages conveyed by signals. Compared with indications, signals are signs transmitted explicitly and openly that constitute the main axis of the discourse. In the course of classroom communication, teachers emit circumstantial indications in parallel with the transmitted signals. The signals refine the understanding of the messages of the scientific concepts being taught in order to make them more meaningful. This study investigates one Physics teacher’s class in a lab in which an empirical activity is guided at various moments through discursive activity based on problem-solving methodology. The paper identifies and qualifies some types of circumstantial indications emitted by the teacher, contextualizing their role in the discursive process during teaching.