An effective way to gauge the breadth of the market is to see the percentage of SP500 stocks which are trading above their 200 day moving average (DMA). As we can see from the chart below a high % of stocks above the 200 DMA indicates bullishness in the market. Further when it falls below 10-12 region and then reclaims 20 it is a sign of further bullishness ahead. And once it sustains above 80 it is a sign of extreme bullishness.
Observe the periods 2011 and 2019 when it went below 10-12 and then reclaimed 20. Calm periods of bullishness followed. A similar thing has happened in 2020. Markets are suggesting the next few years may be bullish for the broader markets. Currently it is in the low 60s and there is still some time before it conquers the 80 mark. We will keep an eye on this indicator.