International Encyclopedia of Systems and Cybernetics

While a sign is simply something which may carry a meaning for some definite observers with the needed background, a symbol is a "something that represent something else by association, ressemblance or convention…" (AMERICAN HERITAGE DICTIONARY, p.1302).

According to C.S. PEIRCE; "A sign is either an icon, an index or a symbol. An icon is a sign which would possess the character which renders it significant, even though its object has no existence; such as a lead-pencil streak representing a geometric line. An index is a sign which would, at once, lose the character which makes it a sign if its object were removed, but could not lose that character if there were no interpretant. Such for instance, is a piece of mould with a bullet-hole in it, as sign of a shot; for without the shot there would have been no hole; but there is a hole there, whether anybody has the sense to attribute it to a shot or not. A symbol is a sign which would lose the character which renders it as sign if there were no interpretant. Such is any utterance of speech which signifies what it does only by virtue of its being understood to have that signification" (in J. HOOPES, 1991, p.239-40).

D. Mac KAY gives other examples: "An overcast sky "means" that rain is inminent." (1969, p.88) This is just an observed situation, which need not necessarily and is not intended to exert a preselected influence on the observer and induce him to some specific behavior.

On the contrary, when learning the national anthem, anyone is supposed to adopt a dignified and at times quite precisely, specified attitude because the anthem is a symbol of the mother country to be respected and honored.

In short, signs nature, perception and use are an unavoidable bedrock for systemics. This explains the precursor role of linguists, semioticists and semanticists in systemics.