Some Stock Market Investors Find This Chart Troubling

Stocks are surging today, and the S&P 500 isn't too far from its September 18 all-time high of 1,729.

But of all of the warning signs skeptics point to, this is one of the more unusual ones.

From Jefferies' Sean Darby, this chart show the number of S&P 500 companies hitting a new all-time high on a given day.

"Judging from previous rallies, there have been much fewer companies posting new highs lately," said Darby.

Unfortunately, this chart doesn't track the number of stocks that are trading just below their highs.