Signs and symbols only have the meanings that are assigned to them by convention. They do not exist in a world of their own where they have either significance or power. They exist as signs and symbols only by the implicit agreement of their users.
Take the word "cat" for instance. If any two of us, we all seem to be fluent in English, were to have a conversation about the fuzzy little pet that likes to push his way onto my lap while I'm at my computer, we could use the word "cat" to refer to him without any explanation or discussion of the word's meaning.
By convention, the word "cat" can refer to fuzzy little mammals of a particular type. We can modify it with any number of other words that are by convention allowable: "fuzzy cat", "my cat", "pain in the *advertiser censored* cat", etc.. Those meanings exist because we have a complex structure of which they are a part which has evolved to allow us to communicate with one another.
That structure itself only exists through the active participation of a particular group of people acting together in a particular context, at a particular time. None of those things are fixed, and actually are constantly in flux but they are all more or less necessary for any mark, object, sound, or collection of any of those to be a symbol or a sign.
"Cat" as described above is actually two different things, because I wrote of a conversation. The set of marks use to write "cat" is itself associated with the sound we use in conversation to refer to that animal again by convention only. It is also flexible, since we would likely still recognize it even if spoken in any of the wide range of accents that participants on this forum might have. That sound pronounced køt or kat, according to my Apple dictionary, could also be associated with spellings such at khat or ghat and could refer to any number of other things depending as usual on where, when, and among whom it's being used. If we prepend another descriptor, like Hobie to cat, we refer to a sailboat.
"Cat" then, we can easily see means nothing on its own. It has no history, it has no baggage. The same is true for signs and symbols in general. The chief distinction between signs and symbols is that signs are entirely abstract while symbols have some sort of recognizable relationship to what they are used to symbolize. A stop sign is a sign because there is nothing other than convention that associates red octagons with stopping. Red can be a symbol of sacrifice, because sacrifice not uncommonly involves the spilling of blood, blood is red, and so on.
It is also clear that stop signs have nothing to do, unless we were to go through some complex rhetorical gymnastics (of course not unknown in these parts), with sacrifice. Red then can be seen to carry no universal symbolic meaning. The same is true of any other symbols. Their meaning only exists by agreement. If we don't agree, they don't mean anything and they can't accidentally or unintentionally have meaning either.
