LEWISTON — Counterfeit bills circulating through the Twin Cities over the past couple of weeks started out as drug money, police said Friday.

Several thousand dollars in bogus $20, $50 and $100 bills have made their way to convenience stores and shops, supermarkets and department stores in Lewiston and Auburn. Many sharp-eyed cashiers have spotted the fake money before it was too late, but others put the bills in their tills only to discover later they’d been duped.

“It’s almost on a daily basis,” Lewiston police Detective Lee Jones said Friday.

He said the counterfeit money popped up during drug deals and illicit transactions, in which one dealer was trying to rip off another. The dealers stuck with the bad bills try to launder them by making small purchases at stores where busy cashiers might not notice.

“If they cash a (counterfeit) $100 for a $3 item, they’re losing quite a bit of money,” Jones said.

The bills are easy to spot by people who handle a lot of cash, Jones said. That’s why they’re never taken to banks or other financial institutions.

“Most of the time, they’re not cut straight or they’re smaller,” he said. “The paper is going to be really thin or really thick. It’s usually poor representations of money.”

Often, store clerks can identify fakes before the customer hands it over, Jones said.

A person in elementary school probably would be able to recognize it as bad money. “It’s that bad,” he said. Jones said the holograms used on money and other documents to prevent counterfeiting are never right on the fake bills.

Different stores have different policies for responding to bad bills, he said. He advises cashiers to tell the customer that the bill looks counterfeit and police will be called.

Often, the customer will grab the fake money and bolt, Jones said, a sure sign the customer is aware of its inauthentic nature.

One man came into a store and tried to pass off a bogus $50 bill. The cashier said he couldn’t take it. The customer, who was trying to purchase two Twisted Teas threw a $5 bill on the counter and left quickly, grabbing the $50 bill and the drinks, Jones said.

“Obviously, he could have just paid with the $5 bill, but he was trying to circulate it,” Jones said. Some holders of the bad bills will ask people on the street to break them, he said.

“That happens quite often, too.”

Roughly $1,000 in fake $100 bills has been successfully passed along, Jones said. That figure could be higher. Not all of the successful transactions have been reported to police, he said. About $1,000 worth of the bad bills have been turned away, he said.

As he continues his investigation, he is working with the Secret Service, which eventually will take possession of the evidence, he said.

Before 2008, the occurrence was rare, he said.

“It used to be unusual to get a counterfeit bill,” he said. “It was a once-in-a-blue-moon type of thing.”

But since the severe downturn in the economy, counterfeit money has become a more common sight, both in Maine and locally. The bad bills come in waves, four to five times a year, he said, sometimes along the coast, sometimes closer to home.

“People get desperate and they think maybe they’re going to make some money.”

Even with the trending frequency in counterfeit money, its effectiveness pales in comparison to other fraud schemes, such as Internet and phone scams, Jones said.

Police have made no arrests, but they expect to.

“I’ve got some leads, so, hopefully, in the next week or two maybe we can make some arrests,” Jones said.

Whether or not the attempt to pass counterfeit money is successful, the crime of aggravated forgery has been committed, Jones said. And it’s a felony.

He urged store cashiers to be diligent about checking their money.

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