Goldman's bear market indicator is at a rare 73 percent, its highest level since the late 1960s and early 1970s.
At such levels, the tool predicts a zero average return over the next 12 months and a "substantial" risk of drawdown.
The indicator is "flashing red," wrote Goldman chief global equity strategist Peter Oppenheimer. "Historically, when the Indicator rises above 60 percent it is a good signal to investors to turn cautious."