This Brief Report addresses the fundamental role that sign language plays in the mathematics classroom of deaf and hard-of-hearing (DHH) students. Selected findings are gathered from an ongoing study of signs and gestures used by DHH students and their teachers when encountering and communicating mathematical ideas at a German special-needs school that focuses on hearing and communication. The focus rests primarily on iconic aspects of mathematical ideas as reflected in the gestural–somatic modality of sign language. A categorization of iconicity in mathematical signs as used by the students is presented and used to reconstruct a case of meaning making in a Grade 5 geometry classroom. Insights gained from these observations lead beyond the DHH mathematics classroom by providing new perspectives on the interplay between language and communication, individual experience, and shared conceptualization.