The S&P 500 posted a gain in each of the first five trading days in 2010. It was up 2.74%. That is just the fourth time that has happened since 1928, according to Howard Silverblatt, senior index analyst at S&P indices. The first five trading days has been a fairly accurate barometer for forecasting the direction of stocks in a given year. It has about a 75% success rate in terms of predicting whether stocks will be up or down at yearend, according to Dan Greenhouse, chief economic strategist at Miller Tabak. Since 1950, there have been just five occasions when the indicator failed to predict the direction of the market, according to the Stock Trader’s Almanac.