In the field of E-learning, the goal of researchers in knowledge acquisition and transmission is to produce e-services that are genuinely useful, that is to say, perfectly adapted to their end-uses. Here, we will deal with the specificities of learning how to play a musical instrument for which the quality of learning depends on the quality of teaching methods. In this context, semantic management of tacit and explicit knowledge from experts and books is not enough. Knowledge engineers must also capture live interpretations of expert musicians to illustrate the lesson to be learned. To enhance these significations, Sign management is a concept that has more relevance than Knowledge management: it aims at indexing multimedia contents (i.e. annotations) on different on/off-line supports with formalized textual information (i.e. scores) in order to better share interpretations and viewpoints. In this paper, we explain our concept of Sign management in the new digital and relational ecosystem. We then describe an iterative method based on a Creativity Platform that establishes end-uses as the criterion by which e-services are developed. The Creativity Platform serves to better understand the transformation of a given tool (proposed offer) into an instrument (motivated demand), which, in turn, motivates the supply that is produced to meet the demand. We illustrate our method based on activity theory by using an example of instrumental e-learning, the e-guitar project. Finally, we discuss the pragmatic results of our co-design experience with end-users.