Counterfeiters, it seems, have their own kind of holiday spirit. Where shoppers see long lines, stressed cashiers and shrinking billfolds, funny money hustlers see opportunity.

U.S. Secret Service agent Michael Seremetis wants to ruin their holiday fun.

From the federal agency's Long Island office in Melville, Seremetis and others catalog and investigate the $40,000 or so in counterfeit bills netted weekly in Long Island stores and banks. It's a number he expects to rise as cash registers go into holiday overdrive.

"There is typically a spike during this time of the year," Seremetis said. "The chaos in the department store, the cashier is trying to move people through quickly, not paying attention, they take advantage of that."

Seremetis pulled a crisp $100 from a plastic sleeve. Benjamin Franklin's lips are pursed in appropriate detail. Shiny numerals wink in the light. An embedded ribbon reads rightly: USA 100.

But with the bill laying on a desk, Seremetis pointed to the watermark of Franklin's face floating on the right side of the bill. "That should only be visible when held up to the light," he said. With a bit of added vigilance and a few extra seconds at checkout, "merchants should be able to spot that easily."

While about three-quarters of counterfeits are now made with digital scanners and inkjet printers, the better fakes are made on commercial offset printers. Combined with special inks and chemical paper treatments, the bills can plausibly mimic micro-type and other security features of most modern U.S. bills, but still typically contain multiple recognizable defects.

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Starting in 1996, the U.S. Department of Treasury has phased in new $100, $50, $20, $10 and $5 bills, with many new security features (the workhorse $1 and the reclusive $2 remain in old-fashioned styles). By far the most prevalent counterfeit is a $20 made on common digital equipment.

Seremetis says he hopes Long Islanders will be on the lookout this holiday season for a particular $50. The relatively sophisticated fakes, containing a trademark "C 3" and "C 1" in upper corners of the bill face, are believed to come from a single overseas maker and have been found in large numbers on Long Island and in the tri-state area for several years. While there have been several arrests related to the bill, he said, "Obviously we would like to get to the original source of these notes."

Of the $870 billion in U.S. currency in circulation worldwide, far less than 1 percent is phony, according to the agency charged with policing the nation's currency. Last year, the agency found $64 million in bad bills had been passed domestically and another $6.4 million overseas, Seremetis said.