Relative strength could overshoot and/or prices could move higher while strength declines, that would be the negative divergence to look out for. The RSI should also dip below 70 for confirmation. For more information on the RSI (relative strength index) Stockcharts.com and Investopedia have information. Here are chart snapshots you can find at Stockcharts.com. Also watch that 38.2% Fibonacci retracement level on the $SPX at 1,014.