Today's wild day cause the Volatility Index ($VIX) to spike up above 35 for the first time during the current market uptrend. The follow chart shows what the market has done in the past when that signal has occurred:
Click here for a live version of this chart.
In the late 90's the market ignored the signal and kept climbing until May of 2000 when $VIX gave the signal a third time (or came really close to giving it, we only have close data for $VIX at that time).
In 2007, the same signal occurred twice just before and after the market topped.
Today, the signal occurred again. It will be very interesting to see how significant the signal is this time.