It all began for purely practical reasons, said Ferranti-Dege owner Tony Ferranti, but using the two-dollar bill has turned into a major advertising gimmick for the photo store on Mass. Ave.

Although two-dollar bills returned to circulation in 1976, no other store in Harvard Square has opted to use them on a regular basis and Ferranti-Dege has become distinct for its use of the bill.

At the rate the nation's supply of bills--last printed in 1976--is going, the two-dollar note will last a long time before it goes out of circulation, said Edward A. Romkey, assistant vice-president of cash services at the Federal Reserve Bank in Boston, which distributes the bills to banks in the area.

"I have a lifetime supply [at the bank] based on what's gone out," Romkey said.

This lack of demand for the bills is just what makes them valuable to Ferranti Dege.

"What it does is make us different," Ferranti said. "So few people are using it that when you give it out, people remember you. It makes us unique and distinctive."

"It's surprising how many people look at it in a startled manner and are very suspicious," he added. Ferranti said that while some people are intrigued by the bills, others ask for one-dollar bills instead.

Some people cherish superstitions about the bill, Ferranti-Dege employees said. "People thought they were bad luck," said James J. Casey, assistant manager at Ferranti-Dege. He said one of the reasons the bills were originally discontinued in the 1950s was because many people associated them with gambling and the underworld, partly because they were commonly used for placing two-dollar bets at racetracks.

But Casey added with a smile, "We say it's good luck."

The bill works well as an advertising ploy, he said. "I've been in stores where I give a two-dollar bill and people say 'You've been to Ferranti Dege,'" he said.

The store tried using Susan B. Anthony silver dollars for advertising purposes in the late seventies, but discontinued their use because they looked too much like quarters and were impractical, Casey said.

Using the bills also saves the store money, Casey said, as it makes it easier to give correct change and prevents large losses from theft, because if two-dollar bills are used, twenties must be kept under the cash drawer and would-be thieves can't reach over the counter and grab them.

The store acquires its bills at BayBanks Harvard Trust, and officials at BayBanks and Ferranti-Dege is the only business in the Square that orders two-dollar bills on a regular basis. The bank goes through about 2000 two-dollar bills every other week, according to BayBanks officials.