A market theory that states that a white Christmas in Boston will result in rising stock prices for the following year. For example, in Christmas of 1995, Boston received snow and the following year, the S&P 500 increased by more than 20%. Taobiz explains Boston Snow Indicator As you may have guessed, there is no logical correlation between whether there is snow in Boston on Christmas and the performance of the stock market. Any incidence of a white Christmas in Boston and bullish market performance in the following year are purely coincidental. This may be why this indicator is also referred to as the "BS indicator".