Check this out. Is this a case of extreme overfit, or a trading (rather investment) opportunity. EMA13/EMA34 Cross - Weekly SPY
They don't always look that good in hindsight, but there's the problem with crossovers. No guarantee that you wouldn't get chopped to pieces on the next hanful of signals.
The EMA combinations are good for showing you where support and resistance are in a sustained trend ... they are not good when used as a crossover signal by themselves. Hope that helps.