Every symbol is made up of various parts. After all, one thing symbolizes something else, so we at least need the symbolizer and the symbolized. We could say one thing gives meaning to the other thing that receives the meaning.
Four essential parts of a symbol
The source, the thing that gives meaning
The output, the other thing that receives the meaning
The medium, the path through which energy flows from source to output
The energy, the actual physical thing that moves from the source, through the medium to the output.
A few important points:
Nothing originates energy-flow.
Two things can symbolize each other. So we can envision the energy flowing back and forth between them, and they take turns being source and output.
It's a common mistake to think of a symbol in terms of just one or two of its parts while ignoring the other parts. To avoid confusion, we must always consider all the parts of a symbol.
Can we say a river is a symbol of its mouth? If you want to. Symbols are inherently subjective, which means a thing can be a symbol for one person and not a symbol for another person.
A simple scenario as an example:
I give meaning to a token. I declare that the red stop sign means to stop. So here's how I interpret this:
Light from the stop sign enters my eye, and my brain forms an impression of the stop sign. This impression is a neural construct that my brain made by building connections among neurons. This means the next time I see the stop sign, I can remember my previous experience of it and recognize it. So at this point, the stop sign is the source, and my neural construct being activated is the output.
I decide the stop sign should mean that I stop. In other words, I have built another neural construct. Now the first neural construct (by which I recognize the stop sign) is the source (when it is activated), and this new neural construct is the medium through which energy flows to the output, which is my activity of stopping.
So there are two kinds of symbolism here. First I recognize an object, and then I decide what to do whenever I encounter that object. In the first case, my neural construct is the output, and in the second case my other neural construct is the medium.