Here is a simple list of month symbols for futures contracts. Today we are leading up to Decemeber which has been the "Z" symbol. Generally a shift occurs before the month.
FULL RISK DISCLOSURE: Futures trading contains substantial risk and is not for every investor. An investor could potentially lose all or more than the initial investment. Risk capital is money that can be lost without jeopardizing ones financial security or life style. Only risk capital should be used for trading and only those with sufficient risk capital should consider trading. Past performance is not necessarily indicative of future results.