Amazingly enough, your method is essentially the same as was used to make the blade of Mann’s Global Warming Hockey Stick. ...Really.
I just googled for it and found this tidbit:
By now, many in the sports and financial communities are aware of the "Super Bowl Indicator". Created in part by "longtime Wall Street guru" Robert H. Stovall, the Super Bowl Indicator claims "if an old AFL team wins the Super Bowl, the stock market will decline during that calendar year and if an original NFL team wins, the Dow Jones industrial average will rise". Although some pundits have sought to debunk this predictor, it still carries an over 80% success rate.
Actually, I thought the success rate was closer to a 100%. There must have been some bad games since I last looked at this indicator.