MA 3 and MA 5 crossover as SPX buy and sell signal has been working well for long term investing. It can avoid big drops and can capture big gains. In a bull market, it may not beat buy and hold, In a bear market, it does not lose as much as buy and hold.
if the red cross stays on August 31, 2015, it will be an official sell signal. This may or may not mean a big drop is ahead, the point is avoid potential big drop that can be very damaging.