Prototyping plays various roles in software engineering: it can function in an exploratory way in order to gather requirements, or generate an artifact that, through iterative cycles of development, leads to final delivery of the product or system. According to literature (Beaudouin-Lafon, M., and W. Mackay. 2007. Prototyping Tools and Techniques. In Human Computer Interaction Handbook: Fundamentals. CRC Press.; Lim, Y. K., E. Stolterman, and J. Tenenberg. 2008. The anatomy of prototypes: Prototypes as filters, prototypes as manifestations of design ideas. ACM Transactions on Computer-Human Interaction (TOCHI) 15 (2): 7.), a prototype can be described as an incomplete but flexible communication tool for a design idea, both manifesting and filtering interesting aspects of the original idea. On this basis, we propose a Peircean definition for this tool: a prototype can be considered as a complex set of signs, or better as a text, because each of its features literally stands for corresponding features of the final artifact, foreseeing particular aspects or the overall capacity of the outcome. But what happens when stakeholders involved in a project have no or little competence in tools and technologies discussed? Can they correctly interpret a prototype? To answer this question, we propose a Discourse Analysis (Duranti, A. 1997. Linguistic Anthropology. Cambridge, Mass: Cambridge University Press; Potter, J. 2004. Discourse analysis as a way of analyzing naturally occurring talk. In Qualitative research: Theory, Method and Practice, edited by D. Silverman, 200-221. SAGE; Schegloff, J. 1989. Harvey Sacks' lectures on conversation: an Introduction/memoir. Human Studies 12: 185-209.) of a co-design session with elders of a daily centre for frail adults in Rome. In this context, we could observe how interactions between the material aspect of the prototype (i.e. the product itself) and its intended meaning (i.e. its significance) can produce distortions, in the form of aberrant interpretations or even a complete lack of comprehension. During this communication breakdown, prototypes lose their connection to the features and behaviors of the product: the relation between representamen and interpretant is lost.