Investing - Theory, News & General • Ticker decoder ring

Is there some document that summarizes any standards for ticker symbols? It seems like mutual funds end in X and money market mutual funds end in XX. Don't know if that's a rule or just a common convention with exceptions. I think bankrupt companies end in Z. Companies seem to try to begin their mutual fund tickers with the letter of their company like F for Fidelity and V for Vanguard. ETF tickers seem to be all over the map along with common stocks who come up with cute names for the fund or company. Stat