Lets say you're starting a new coin. How do you reserve the 3 or 4 letter code for the coin that all coins seem to have. And with whom do you register it? And what's the purpose or significance of the code?
There's no place to reserve, you can just search to make sure no exchanges have that symbol. It is the wild west, so do what you want. You can even have the same symbol with another coin, but if exchange will list it they will change it to an unused one.