AUSTIN, Tex. — Last Wednesday was another good day to make money on Wall Street: Stocks pushed up, interest rates were at rock bottom and the VIX gauge of investor unease was again trending downward.

But as investors celebrated yet another bounce-back from a market slip, Christopher Cole, a trader who runs a hedge fund here that makes bets on various forms of financial apocalypse, spotted something amid the sprawl of data and code that decorated the wall of screens before him.

“Optically, volatility is still very low, but fear is increasing,” Mr. Cole said, pulling up a chart on one of his six trading windows. It showed that in the months beyond the 30-day period measured by the Chicago Board Options Exchange’s VIX index, investors were expecting some violent moves to come in the stock market.

Betting against a flare-up of such turmoil has been one of the longest-running and most profitable trades in recent financial history.