NYA*TICK for sentiment

NYA is the price of the NYSE index, a broader cut of the market than SPY,QQQ or DIA alone.
TICK is the difference between the number of green and red issues in NYSE. As such, it measures the breadth of NYSE, a broad index.

Multiply the two. Focus on the low's. The trendline from years ago (left chart) predicts the recent market drop almost to the day (right chart)