For millions of Americans, watching and waiting is the new day-trading-and the trillion-dollar question is when they'll feel fully comfortable investing in stocks again. In the U.S. alone, investors still have nearly $900 billion parked on the sidelines, according to Thomson Reuters. The tide finally began to shift this spring, when an upward bounce in the markets and upbeat forecasts from luminaries like Federal Reserve Chairman Ben Bernanke helped lure some investors out of hiding. Financial advisers say they're seeing a surge of inquiries from clients about stocks. "It's about 15 to 1 in terms of calls from people who want in versus out," says Tom Hepner of Ruggie Wealth Management. And sentiment among fund managers recently shifted from "apocalyptically bearish to reluctantly bullish," according to a survey by Banc of America Securities-Merrill Lynch.

The key word, though, is "reluctantly." The recent rallies have eased some investors' fears, but it will take a lot more prodding for others to get over the crash of 2008. Although the pros know that historically, stocks recover long before the rest of the economy, nobody wants to suffer more losses by getting in too early. Or, for that matter, too late: Some who missed out on this spring's stock gains now fear that the market has no more gas in the tank. Misgivings like these explain why pros and amateurs alike obsess over their favorite economic indicators-from "TED spreads" (it's a bond thing) to taxi-line wait times-trying to decide if the glimmers of improvement can translate into a lasting recovery.

With that in mind, SmartMoney magazine polled a slew of economists, managers and strategists to find out which signals will give them confidence that the worst is truly behind us. No single one of these indicators is a surefire green light. While any number of statistics-like weekly unemployment claims and surveys of sentiment among manufacturers-have helped to signal rebounds from the 10 recessions since World War II, few have hit the mark each time. TD Ameritrade Chief Investment Strategist Stephanie Giroux says that before she utters the words "a new bull market," she needs to see "clear evidence on multiple fronts that the economy is starting to grow again." For investors still smarting from last fall, waiting for multiple "go" signs has an appealing logic. Before they feel confident about the stock market's risks, they want to feel like the other elements of their economic lives are secure.