DETROIT (WWJ) – As police in Toledo investigate counterfeit $5 bills that have passed through three businesses in the past week, should metro Detroiters worry their wallets could contain bogus bills?

Douglas Zloto with the U.S. Secret Service in Detroit says it’s not likely.

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He told WWJ Newsradio 950’s Zahra Huber it’s rare for people to come in contact with counterfeit cash.

“The amount of counterfeit in circulation is very, very small; and the normal Detroit citizen living in this area…it would be rare for them to find that they would be in possession of a counterfeit bill,” Zloto said.

Zloto said there are multiple security features on bills that show they’re real.

“Every bill, $5 or higher, has certain security features — one of which is a water mark. So if you hold the bill up to the light you will see a watermark,” he said. “If the money does not have a water mark, that is a potential indication you have a counterfeit bill.”

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“The other (feature) is a security thread that runs through the paper, Zloto said. “Other features that you can look for are, in our genuine paper we have red and blue security fibers throughout the bill…The counterfeit money that we see mostly passed here in the Detroit area is not gonna have those red and blue security fibers.”

Some of these crooks creating counterfeit cash, he said, are getting smarter.

Zloto said the counterfeit protection pens you may see being used at store check-outs react to the paper itself, “And sometimes the criminals will try to mask the effects of the pen by putting a substance on the paper so that the ink from the counterfeit detection pen will not seep in the paper to react.”

Zloto said, by law, all banks are required to send into the Secret Service any bills believed to be counterfeit. The phony bills are cataloged and investigated to identify patterns and new tricks.

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Zloto said the Secret Service is working with Toledo police on the case. So far, he said, there are no leads.