The thing about symbols is that they can mean different things to different people... and to understand the meaning behind it you have to know who used it and in what context it is used. I could draw a symbol that catches peoples eyes and tell them it means one thing while it actually represents something totally different. Its very hard to research back to the original meaning of a symbol and know for sure exactly what it means for a number of reasons: the above mentioned being one, the fact that many symbols go back thousands of years and are picked up along the way and used to represent something totally different (for example, research the swastika symbol and the original meaning in Hindu and early Christianity before Hitler used it and gave it a bad symbolism), and then there is what it means to each person.
You have to narrow your question to things like: "What's the original meaning of ..... symbol?" or "What was ..... symbol thought to have represented to this period of time or this religion?", etc.
I wish I could give you a definitive answer but I'm afraid there are at least several different well known meanings to that symbol... and to top it off, many symbol's true meaning are only known to certain "enlightened" people. Symbols, for thousands of years, have been used as a sort of code that needs to be decifered, but many times the initial best guesses are way off base. Many sy books are created to give the impression of looking like one thing while if you look at it with a different perspective it isn't anything like what most people would see in it. To give an example of a few of the above mentioned problems you face when trying to decided a symbol, think about the cross we all know. Its thought by millions to just represent the crucifixion of Jesus Christ... that's it. But the cross symbol is thousands of years older and has been found in the earliest of worship of the sun....It represented the summer and winter soltice. It has also been used as a symbol for the cardinal directions of North/South-East/West and as Earth, Air, Water, Fire on the respective ends of the cross with Spirit or Ether in the middle. Now, this symbol, if thought of looking at it from the top looks like a cross, but if you can imagine looking at it from the side, with the Spirit/Whether point in the middle raised up above the other points. now draw a line from each of the four corners of the cross to each other and up to the Spirit/Ether/Whether point raise in the middle and you will see that it turns into a pyramid! Its all about perspective, where,when,why and who started it or made it, and what YOU see in it.
I hope I explained it so you could understand and follow along to visualize what I was talking about.
In the end, it could very well represent Earth, Air, Water, Fire, Spirit/Whether and the circle would represent the connecting of all of those things with Spirit/Whether being above all... much like the pentagram but just a different representation and look. Or it could mean something completely different! What's it mean to you? Its your perception that counts to yourself.