If you buy the idea that the Japanese yen is a good proxy for risk appetite
in the market (and I do), then this chart is probably one of the most important ones out there. It shows the performance of Japanese yen futures. A move UP indicates that the yen is rising against the dollar, and that risk appetites are decreasing. A move DOWN means the opposite -- that the yen is falling and that risk appetites are increasing.
As you can see, we're testing the broken downtrend that dates all the way back to last May. should we break through, it would likely be beneficial for asset values. The opposite also holds true. This post
helps explain why. For more, you may also want to check out this Currency Currents bulletin
(PDF link) from a sharp market watcher by the name of Jack Crooks.