Looping in the others, October 2011 and September 2012 are the clearest signals with the most immediate negative performance.
As such, I think an argument can be made when these ratios align at a low level it indicates widespread complacency and a material selloff is about to begin. But I think the argument that "the market will just shrug off these readings after a -2% tip-of-the-hat (or less) and proceed on its way" is equally persuasive.
If anything, PC ratios - take your pick or take them all - are good countertrend cues; but taken in isolation, that's it. They do a pretty decent job of signaling dips and pullbacks. But, there's nothing special about the December 2007 reading on the Total PC above; or on Equity or Index that would indicate the market was about to get kneecapped. One could only say "ah, but *that* one was different!* in hindsight.
One thing I do note when plotting daily readings is they do tend to persist and cluster in the period leading up to a major top. Recall this chart from last night:
That suggests a moving average that is consistently low is more reliably indicative of "complacency" than extreme low readings. Slap a 20 and 50SMA on CPC, for example: The readings are 0.87 and 0.9, v. yesterday's 0.65 close. January-February, August, October, December 2012, February, April, May 2013 and Now all register similar readings - making these results unremarkable, IMO.