Usually I look at this stuff as a contrarian indicator but this actually correlates pretty well with down moves. There's a chart on minyanville since I can't post the article. March, 2012 seemed to be the one outlier.
Yes - especially when VIX option activity doesn't move opposite the S&P. I follow VXX, which tracks short term VIX options. Usually it goes in the opposite direction of SPY almost tick by tick, though not a mirror image - the magnitude of the moves differs. Which way VXX moves more sharply vs. the SPY tends to be an (inverse) leading indicator for the S&P. If VXX trends in the same direction as SPY, that's an especially strong indicator that the S&P is going to reverse direction. Although I haven't seen that happening, for the last day and a half VXX has had a strong upward bias relative to SPY, meaning that it was rising whenever SPY was falling and sometimes rising significantly while SPY was falling slowly, whereas at times it held its ground or declined only slightly while SPY was moving up fast.
This activity is consistent with what you're seeing. Makes me think that people with inside info and/or institutions doing their own independent analysis anticipate that tomorrow's employment report is going to be a stinker.
Also notable is that this morning after 8:30 when better-than-expected claims numbers were announced - both initial and continuing - SPY went *down* and VXX went *up*. That's highly unusual.
Sentiment: I'm convinced that we're in a bear market, and tomorrow is likely to confirm that