Indeed, as the market hits at its seasonal sweet spot, investors have been rushing to jump on board. Historically speaking, December is the market's best month, with average returns both for the S&P 500 and Dow Jones industrial average at 1.7 percent since 1950, according to the Stock Trader's Almanac. The indexes respectively have seen gains of 0.8 percent and 0.9 percent this month.
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In addition, the expected "Santa Claus rally," measured during the last five trading days of December and first two days of January, has produced an average 1.6 percent gain since 1969.
Seemingly in anticipation, U.S. funds took in a combined $36.5 billion over the most recent reporting week, according to Thomson Reuters Lipper. That comes as part of a run that has seen $81.3 billion alone come into the $2 trillion ETF space since October, according to TrimTabs. That's the largest three-month flow ever, topping the influx from July through September 2008.
TrimTabs CEO David Santschi said the strong flows are "very negative from a contrarian perspective." In short, that means overheated sentiment generally signals the end of buying cycles and difficult times ahead. And should Santa Claus fail to deliver, that has often preceded a weak market — as the almanac puts it, "If Santa Claus should fail to call, bears may come to Broad and Wall."
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Looking further inside the trend, though, it hardly seems like optimism is overflowing.
The most recent Investors Intelligence survey, which polls newsletter authors as a gauge of professional investor sentiment, had bulls at 52.5 percent and bears at 15.8 percent, the latter measure being the highest since mid-October.
Looking at individual ETFs since the beginning of October also shows a fairly cautious approach.
Three of the top four funds in terms of inflows are plain-vanilla S&P 500 trackers, with the "Spider," or the SPDR S&P 500, fund leading the way with $27.2 billion, according to ETF.com. Bond funds hold the fifth and sixth positions, with the iShares Core U.S. Aggregate Bond fund taking in $3.8 billion and the Vanguard Total Bond Market attracting $3.7 billion in new cash.
In terms of outflows during that period, investors fled the iShares MSCI Emerging Markets fund, redeeming $4.8 billion, and the Nasdaq-tracking PowerShares QQQ fund, which lost just shy of $4 billion.
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Those results in both inflows and outflows are pretty consistent with the full year. Of the ETFs that track S&P 500 sectors, the biggest money flows have gone to staples, energy financials, utilities and health care. Materials, technology and industrials have seen net outflows for 2014.
"The best performers still have been fairly defensive. It's still a search for yield," Krosby said.
The market also received a recent boost from the Federal Reserve, which indicated after its December meeting that it is in no rush to raise interest rates even though it has ended its monthly bond buying program. Quantitative easing drove the central bank's balance sheet to $4.5 trillion and was seen as supporting the market, but investors seem just as focused on the Fed's maintaining its zero interest rate policy.
"The question is how much more the Federal Reserve can underpin the market," Krosby said. "The market seems to believe that somehow the Fed will do everything in its power to prevent a major selloff."