- Not on a narrow topic, but maybe you have a desire to answer.
Hypothesis. Any material something can be a sign.
Is it possible to give an example of something material that cannot be a sign?
Sign relations are mathematical relations we can use to model processes of communication, learning, reasoning, just plain talking and thinking in general. Anytime we can imagine a triadic relation where one thing, material or otherwise, is related to a second thing in such a way that both refer to a third thing, and that whole relationship is useful in modeling one of the above mentioned processes, then we have a candidate which may be suitable for serving the purpose of a sign relation in the pragmatic conception of the term.