Some market signals aren’t working like they used to. Here’s the one to watch.

A favorite aphorism of the late Art Cashin, Wall Street legend and UBS’s long-serving director of floor operations at the NYSE, is that “no one rings a bell at the top of the market.”

And of course, the same applies to the bottom. There was no clanging to be heard on that day in March 2009, when the S&P 500

SPX hit a low of 666 during the height of the global financial crisis.