The S&P 500 <.SPX> triggered a key technical signal called a death cross on Thursday that could mean more negative moves ahead.

The benchmark's 50-day moving average dipped below its 200-day average in what technical analysts consider a sign that short-term momentum has turned more negative than long-term momentum and could show the current downtrend is pervasive. Both moving averages are currently heading lower.

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The benchmark's 50-day average had last been below its 200-day average in mid October.