I often look at INDEX:MMFI to keep an eye to the momentum of the market in general. For me its like another Advance Decline Line of the TVC:SPX but with a little better information. Now I can see that for the past 6 years, every time that percentage hits more than 84%, the TVC:SPX is in the beginning of really good bull run, but normally is just after a market correction.
The great Mark Minervini recently tweetted "Fundamental backdrop remains bullish. I'm not calling for a bear market, but a run up from current levels with increased bullish sentiment would likely be a selling opportunity before a market correction.". His opinion is one of the most influential in my trading so, I´ll be very careful this upcoming days.