The study of students' use of representations is one of the main topics of physics education research and is guided by the overarching field of semiotics. In this paper we compare two semiotic frameworks, one coming from didactics of mathematics and one from physics education research; the theory of registers of semiotic representations and social semiotics, using the networking of theories methodology. A group of first year university students were audio and video recorded as they discussed concepts relating to thermal energy, a study that will be further explored in an upcoming paper. We find that analyzing the recorded data using two different semiotic perspectives provides a wider interpretation of students' representational use, a descriptive approach to how students use the representations, and an approach to the cognitive aspects of the construction of knowledge. By comparing the theoretical constructs they employ, and how they are employed in the analysis process, we identify constructs that both frameworks have in common, but also where they differ. We have found that each semiotic theory provides a different perspective regarding students' representational use. We also propose that comparing different theories may provide a space for complementing the constructs of each theory and providing a bigger picture to understand students' representational use in physics and other science, technology, engineering, and mathematics education areas.