Every sign refers to or stands for whatever it's a sign of. A sign is anything, including a symbol, that represents something other than itself.
When I say "Where there's smoke, there's fire," I mean that smoke is a sign of fire. I say that a red-and-white-striped pole is a sign of a barber shop, or that the word "rain" is a sign or symbol of rain. To recognize a sign for what it is is to be led cognitively by the sign to something different from the sign itself, that which the sign signifies. The physician Becquerel recognized that certain impressions left on a photographic plate signified something other than the plates themselves. The impressions signified the radioactive character of uranium. If I fail to recognize this pointing characteristic of a sign, I may know many of the characteristics of a sign, but I won't know what it represents, or its importance or its meaning.
So every sign represents something other than itself. And even though one may represent oneself in a court of law, that does not make one a sign of oneself. What is represented in a sign is always an existing thing that is distinct from that sign itself.