The Commens Dictionary
Quote from ‘Pragmatism’
A sign is whatever there may be whose intent is to mediate between an utterer of it and an interpreter of it, both being repositories of thought, or quasi-minds, by conveying a meaning from the former to the latter. We may say that the sign is moulded to the meaning in the quasi-mind that utters it, where it was, virtually at least, (i.e. if not in fact, yet the moulding of the sign took place as if it had been there,) already an ingredient of thought. But thought being itself a sign the meaning must have been conveyed to that quasi-mind, from some anterior utterer of the thought, of which the utterer of the moulded sign had been the interpreter. The meaning of the moulded sign being conveyed to its interpreter, became the meaning of a thought in that quasi-mind; and as there conveyed in a thought-sign required an interpreter, the interpreter of the moulded sign becoming the utterer of this new thought-sign.
Enough of the italics! The next step toward our definition is the consideration that a chain of signs that conveys a given meaning can, in many ways, at any rate, be neither beginningless nor endless. Still, it must be of a mental nature. There must then be some other mental element than a sign that can endow a sign with a meaning: and some one upon which the meaning can be ultimately expended.