Investigators are trying to determine if recent purchases with counterfeit bills are isolated incidents or the start of a counterfeit ring in northern Utah.

Three bills were passed in Layton and Roy since Tuesday, when a JC Penney clerk reported the ink on a $50 bill had rubbed off on her hand.Wednesday a ZCMI clerk at the Layton Hills Mall notified police a counterfeit $100 bill had been passed the day before.

Layton Detective Sgt. Steve Brown said the description she gave police - a white female in her 30s with blond hair - matched that of a suspect wanted for passing a fake $50 bill in Roy 30 minutes earlier.

Police were unable to locate any suspects and are turning the investigation over to the U.S. Secret Service.

Brown said if it is part of a counterfeiting ring, "it's unusual for someone to use different denominations . . . of course, there's no way to know if it's the same person."

Counterfeiters hit the area around the holidays with a flood of crude $10 bills.

That may explain an April 30 incident in which a child who bought a $2 Slinky at a Layton Rite-Aid store was given a phony $10 bill as change, Brown said.

Dennis Crandall, the Secret Service agent in charge of the Salt Lake City office, said his office has several ongoing investigations along the Wasatch Front, but the isolated incidents are not reason for alarm.

"Sometimes we get one of these bursts of activity," he said. "But until we look at the characteristics of the bills, compare them to look for similar characteristics, we won't know if they're connected."

The U.S. Department of the Treasury redesigned $100, $50 and $20 bills to make them harder to duplicate. They have larger portraits and several unique printing characteristics, including a watermark to the right of the portrait that can be seen if held up to the light.

"The government went all out to make these harder to counterfeit, but now people aren't used to what they look like," Crandall said. "They're ugly. They look like Monopoly money. Even (Benjamin) Franklin looks a little menacing."