Did you know that the word "symbol" and consequently "symbolism" comes from the ancient word "σύμβολον" which was an ancient practice for mutual recognition either between two known people or even two lovers?
As people have guessed the word "symbol" is Greek but it comes from an ancient practice, something that can be traced even in plays and myths? It was a sign of mutual recognition or a guarantee of identity between two people. And as always the most frequent use of it would have been some cheap and easy to find material such as knuckle bones.
In Euripides's "Medea" Jason confronts his previous wife and expresses his will to help her and then he says that he will provide a "symbol" for her:
ὡς ἕτοιμος ἀφθόνῳ δοῦναι χερὶ ξένοις τε πέμπειν σύμβολ᾽, οἳ δράσουσί σ᾽ εὖ. I am willing to give you a helping hand and also send tokens to people for hospitality, so that they will treat you well
(Translation by me)
The practice went as such; one knuckle bone or some other piece of pottery usually, would be cut in half and one half would be given to one person and the other to another so when the two people met and they joined the two halves, that would be proof of identity. In case of hospitality one person (in this case Jason) might as well wish to sent a friend or family member (in this case Medea) to someone they know and trust but that third person is not aware of who their friend or family is. So the benefactor would be cutting a token in half and offer one half to their friend and the other half to the intended host so that when the two would meet, they would have a mutual recognition
The word coming probably from the verb "συμβάλλω" which has many different ancient interpretations but in this case it would be "to compare" or "to show side by side"
The mutual recognition sign of course is not always physical but also sometimes it can be some signal or other. Who can convince me that the whole "wedding bed discussion" between Odysseus and Penelope in the Odyssey is not some form of "token" of recognition? Both sides require the other to give them what they got, something they can compare to each other.
The essence of tokens representing this union or relationship or even hospitality between two people I would expect is what gave the word "symbol" its meaning. Because it symbolizes (yeah pun totally intended) the bond or the two people joining in one or mutually recognizing each other. The practice was also probably used for mutual recognition of lovers which also led to the exchange of tokens of love between lovers such as pendants, rings, kerchiefs and others
Disclaimer: Of course it needs to be added that proofs of recognition were not something invented by the Greeks. Probably every single nation in the world practiced it with some essence of proof of identity, the carrying of seals or sealings and so on and so forth. I mentioned the specific practice because it has a certain intimate essence to it which I personally love to see not just the official recognition process through letters epistles etc but through the more intimate practice of two people that share some form of bond.
So the next time you share a friendship bracelet or a two halves heart pendant with someone else have in mind that you might be practicing an ancient Greek practice hahahaha
