The signs of market fear are everywhere, from deep-pocketed hedge funders on Wall Street to mom-and-pop investors in flyover country. A year after the market reached record highs and it looked like there was nothing that could stop what has become the second-longest bull market in history, market participants are pulling money off the table and heading for cover. Consider: Hedge funds are at their lowest net long position in four years, at 44 percent, after hitting a record long of 57 percent in early 2015, according to Goldman Sachs.

Money is draining again from equity funds after a period of reversal. Equity-based funds (both mutual and exchange traded) have seen outflows approaching $100 billion in 2016, according to Bank of America Merrill Lynch.

The outflows come at a time when the retail crowd is feeling the heat as well. Bullish sentiment dropped to 19.3 percent in this week's American Association of Individual Investors survey, its lowest level since mid-February and only the ninth time since 1990 that optimism fell below the 20 percent mark. A combination of unease over the path of central bank policy both in the U.S. and abroad, the possibility of a destabilizing British exit from the European Union, and tepid economic growth have investors unwilling to commit new cash to a market that appears at least somewhat overvalued.

"In reality, it's still the fear of the unknown," said Michael Cohn, chief investment strategist at Atlantis Asset Management. "The fact is, nothing has really changed. The fear out there is that there is another shoe to drop somewhere down the road."

On a more micro level, there are a variety of explanations both for investor apprehension and the weak market performance that has seen the drop nearly 3.5 percent over the past 12 months as of Thursday's close. Hedge funds, for one, have been battered by wrong-way bets in the long-short category, with stocks that managers bet against strongly outperforming the most-owned long bets, according to Goldman. Hedge funds within the Goldman universe — accounting for $1.9 trillion in the $3 trillion industry — have lost about 1 percent for the year. For individual investors, popular names like Apple have gotten crushed while energy, which became kryptonite after oil's fall, are the leaders in the S&P 500. The top five individual performers in the index are all energy-related, and the sector itself was up 9.7 percent in 2016 as of early Friday trading, second only to utilities. Investors have pulled $95.8 billion from equity funds this year, the bulk from mutual funds ($82.7 billion) but ETFs also have surrendered more than $13 billion, according to BofAML. There is also the weak corporate earnings picture, down 7.1 percent in the first quarter.