"There is little consensus whether good news is good or bad right now, with the indicators that I watch showing everything from fully bearish to fully bullish," said Randy Frederick, managing director of active trading and derivatives at the Schwab Center for Financial Research.
An upbeat November jobs report sparked a rally in equities on Dec. 6, yet a week of mostly solid economic data drew a negative reaction from the stock market in the week that followed.
"It doesn't make a lot of sense. If good news is good news, it needs to stay that way," said Frederick. "Given the mixed indicators, I am not sure we know what the market wants."
"Debate will be running high through mid-day Wednesday about whether the Fed tapers or not at this FOMC meeting. If the averages trade higher today, tomorrow and Wednesday morning, then it could become a 'sell on the news' no matter the decision," Elliot Spar, market strategist, at Stifel, Nicolaus & Co., wrote in emailed comments Monday afternoon.
While arguments can be made for the taper to begin sooner rather than later, Frederick believes the fact that core inflation remains well below the Fed's 2 percent target rate will give it room to delay cutting its asset purchases, and puts the odds of a December move at less than 50 percent.
Frederick is less confident about making a prediction on Wall Street's reaction, whatever the Fed decides: "I think we'll get a big move, I just don't know in which direction."
—By CNBC's Kate Gibson