If the Washington Redskins win the week of the election, this means a win for the incumbent party. This has held true since 1936.
Whoever's Halloween mask sells the most will be the next president. (If more kids want to be Obama than McCain...)
When companies produce 'competing' products, whichever sells the most is supposed to predict the winner. For example, if a company has cups with images of Obama and McCain in 2008, the one which outsells the other would be a predictor.
If the Dow Jones Average gains over the time from August to October, this predicts a win for the incumbent.