U.S. stock indexes are drifting on Wednesday after the Federal Reserve decided to keep interest rates where they are.

Under normal circumstances, a pair of dissents in favor of a rate cut would be taken as a sign the Fed is taking a dovish turn, Tom Essaye, editor of Sevens Report Research, wrote in a Tuesday note. It would be signal that policymakers are moving in favor of easing, making a reduction at the next meeting a more likely event.

But one stock-market indicator suggests the indices could be in store for another substantial decline in price in the not-too-distant future. It just reached a level seen only once before in history, and it has a flawless track record of predicting significant downside in stock prices.