A symbol is an indefinite expression with many meanings, pointing to something not easily defined and therefore not fully known. But the sign always has a fixed meaning, because it is a conventional abbreviation for, or a commonly accepted indication of, something known.
Jung establishes the foundational distinction between symbol and sign, arguing that symbols are irreducibly polysemous and cannot be collapsed into fixed semiotic designations.
, Symbols of Transformation, 1952thesis