US Markets

Cashin: What investors need to watch during selloff

Cashin: Ten-year is the key, will send signals

Investors must monitor 10-year Treasury bond yields to better gauge the severity of the ongoing heavy selloff in U.S. stocks Monday, UBS' Art Cashin told CNBC.

"If you look at yield on the 10-year, it is an important barometer today because it tells you that there are other problems about, and most of that is the emerging markets," Cashin said on "Squawk on the Street."

"We continue to watch the amazing thing of the Fed tapering and yields going lower, so that tells you there may be something out there in the forest that we haven't seen before," he said.

(Read more: Wall St. likely to see emerging market whammy)

Cashin, UBS' director of floor operations at the NYSE, said if yields dip below 2.6 percent, "That would get a lot of people's attention."

He said a trio of factors has made Wall Street nervous on Monday, including weaker-than-expected manufacturing data, concerns about the U.S. economic recovery and worries from emerging markets.

(Read more: Hungary and Russia in crosshairs for rate hikes)

Cautioning investors not to underestimate concerns over currency selloffs in emerging markets, Cashin said the current global situation has potential parallels to the 1997 Asian currency crisis that contributed to the downfall of Long Term Capital Management.

The collapse of LTCM "nearly brought the American economy down," Cashin said.

"So a remote and lightly traded currency almost took the world for a spin," he said.

—By CNBC's Jeff Morganteen. Follow him on Twitter at @jmorganteen and get the latest stories from "Squawk on the Street."