Investment guru Ron Insana says a potential omen from the bond market should cause stock investors to head for the exits

The gap between two-year and 10-year Treasurys is the narrowest it has been all year, the author of four books on Wall Street explained.

A flat “yield curve” is sometimes a sign of an impending slowdown in economic growth.

“Should the Fed normalize rates too aggressively, without a commensurate rise in inflation, long rates could dip further and possibly fall below short rates,” Insana wrote for CNBC.com.

“That condition, known as an "inverted yield curve," has had a very high correlation with slowdowns in the economy. Quite often, it means an impending recession in six to nine months,” the CNBC and MSNBC contributor wrote.

Insana also cited what he called "a couple canaries in the coal mine" as to why savvy investors should be preparing an evacuation route.

"High-yield debt has been selling off for weeks, if not months. Higher-yielding debt reflects not only changes in interest rate policies but also in the future fortunes of heavily indebted corporations," he wrote.

"If a slowdown is coming, the combination of a flattening curve and widening junk bond spreads should serve as a warning about the potential for an economic pullback a few months from now," he wrote. 

"This is just a yellow caution sign at the moment. If the curve should continue to flatten and high-yield spreads suddenly blow out, it will be a flashing red light that should get investors to stop and find the nearest exit sign," he warned.

Insana isn't alone in warning investors.

To be sure, Morgan Stanley is instructing investors to prepare for a "completely flat" U.S. yield curve in the third quarter, a more extreme take on T. Rowe Price Group’s assessment that the spread between two and 10-year Treasuries will zero out next year, Bloomberg reported.

The 30-year yield will hit a record low of 2 percent in the fourth quarter, according to Morgan Stanley, which is below the lowest levels seen in the global financial crisis, "the euro-zone crisis or the height of enthusiasm for ‘secular stagnation,’" writes chief cross-asset strategist Andrew Sheets.

Morgan Stanley recommends betting on the continued shrinkage of the spread between two- and 30-year Treasury yields, targeting the gap to narrow to 10 basis points as one of its top trades.

However,t he flattening Treasury yield curve may reflect “safe-haven” investing and confidence in the U.S. economy and, were the trend to lead to an inverted yield curve, the market would not necessarily signal a pending recession, Atlanta Fed President Raphael Bostic said, Reuters reported.

(Newsmax wire services contributed to this report).