Our accompanying chart illustrates how the relative performance difference between SPY and GSG has soared a mind-boggling 54% over the past year alone. We'll use the iShares S&P GSCI Commodity Index Trust (NYSEARCA:GSG), which follows a broadly diversified basket of commodities futures contracts and the SPDR S&P 500 ETF (NYSEARCA:SPY), a proxy for US stocks. For alert investors, the message is clear: The deflationary action in commodities spells danger for other asset classes like stocks, currencies, and real estate.