Something highly unusual, and potentially quite bearish, has just happened to the stock market.
On Monday, Tuesday and Wednesday, the S&P 500 closed at the lows of the day in three-straight sessions.
It is rare for stocks to close at the dead lows on any given day. Until Monday, it only happened once this year, on March 10.
Now that it's happened three days in a row, some traders are worried.
"Traders like to watch the tone of the close," said Scott Nations of NationsShares. "On Monday it meant things were weak. On Tuesday it meant thing were weak. After three days—the tone is just horrible, there's no other way to look at it. And I don't know what would turn it around."
Mark Luschini, chief investment strategist at Janney Montgomery Scott, said that "on a candle chart, those three declines represent 'three black crows,' a bearish omen."
"Given the last few days' setup, we may retest recent lows at 2035 before the 2010 level becomes apparent," Luschini wrote to CNBC. The S&P closed Wednesday at 2,061.
"The market is far from oversold, so it could have further to go before we might expect to see even a counter-trend bounce," he added.
Of course, not everyone is that bearish.
"At some point the market will not reward dip-buyers, and we will face a more serious correction," said Jonathan Krinsky, a technician with MKM Partners. "At this point we are not ready to anticipate that, but we will of course be watching for signs that 'it's different this time.'"
Stocks indeed fell further on Thursday. Yet the S&P managed to end the day off of the lows set in the morning, so the phenomenon did not repeat for a fourth straight session.
—CNBC's Amanda Diaz and John Melloy contributed to this story.