Quote from travis:
That's correct. I have already tried reversing systems, and they lose both ways.
What that typically tells you is that your particular idea has no edge and probably not much merit. The reason why reversing the signals for a losing system doesn't usually work is because of the bid ask spread and commission (trading costs). Also a true edge is not easy to find. Additionally, losing systems often trade too much and are highly inefficient, so the opposite will also trade too much and be highly inefficient, and also a likely losing system.
Typically the most benefit I get from reversing signals is to clarify which is more appropriate for the particular idea: breakout or countertrend. It can also help you spot the relative strengths or weaknesses of your system.