The fact that semiotics has a major influence on design is widely recognized. Some examples are the recent revival of the concept of abduction in design, introduced by Charles Sanders Peirce to explain the creative part of the design process, or the "semantic turn" by Klaus Krippendorff, or the relationship between architecture and semiotics analysed by Umberto Eco. There are many more examples, but the aim of this paper is to identify the common thread that connects semiotics and ecological design, i.e. the tools that semiotics can provide for this. Specifically, we argue that the basis for ecological design is the concept of Umwelt, which was proposed by the biologist and philosopher Jakob von Uexküll and then reinterpreted by Thomas Sebeok in the field of semiotics and widely adopted by biosemiotics. In other words, the concept of Umwelt - which extends to all living beings the ability to grasp the elements of their surroundings through a process of meaning-making - makes it possible to lay the foundations in the field of design for a more correct interpretation of the ecological relationship between humans and the environment. For design to be truly ecological, one must recognize the meaningful relationships that exist, in the words of anthropologist Gregory Bateson, between mind and nature, or, as the father of ecological design, Sim Van der Ryn, argues, learn from living systems how the natural world works and design accordingly. Some exemplary examples from the field of biophilic design are cited in this direction.