The CBOE Put/Call Ratio is a good measure of market sentiment. Spikes in the put/call ratio usually reflect strong negative sentiment in the market, which can sometimes be used as a contrarian indicator. I put the put/call ratio up against the VIX (CBOE S&P 500 Volatility Index) and the S&P 500 (SPX) below. This indicator can be used with the Equity and Credit Risk Indicators and the Keys to the VIX (1 and 2), which measure rates of change in volatility).
CBOE Put/Call Ratio vs. S&P 500 (SPX) by Dvolatility on TradingView.com
CBOE Put/Call Ratio and VIX vs. S&P 500 (SPX) by Dvolatility on TradingView.com