BOSTON — The blue ‘B’ on the red sweatshirt was instantly recognizable. It was the ‘B’ — short for Boston — on the Red Sox cap, the symbol of a team known throughout the domestic baseball world.

But underneath it, after the words "is for," was Oriental lettering. (“It’s Chinese,” explained one Japanese media member, “but we use it, as well.”) ‘B’ is for . . . what?

“Baseball,” was the answer. “ ‘B’ is for baseball.”

And not just in the Western Hemisphere anymore.

The signing of Japanese star Daisuke (pronounced Dice-K) Matsuzaka to a six-year, $52-million contract — announced with great fanfare last evening before an international press contingent numbering more than 300 at Fenway Park — did more than simply bolster the Red Sox’ pitching staff. It was, the team’s brass said, a move to expand Red Sox Nation beyond the boundaries of the United States, past Latin and South Americas, and into the baseball-rich territories of the Far East.

“This is a long-term commitment [to build a baseball bridge between Boston and Japan] and not a short, one-stop, one-shot venture,” said Larry Lucchino, the Sox’ president and chief executive officer. “Our plan, our hope, is to be active and involved in Japan and to expand our presence there.”

The signing of Matsuzaka — Japan’s best pitcher and described several times, by both his representatives and by the Red Sox, as a “national treasure” — was about as dramatic a step as the Sox could have made . . . both on and off the field.

“From the day we took over this organization . . . we’ve been bold,” said principal owner John Henry. “And this was, I believe, a bold move.”

Bold, indeed. The Red Sox won the rights to negotiate with Matsuzaka with an unprecedented $51.1-million bid to Matsuzaka’s Japanese team, the Seibu Lions. They eventually stared down uber-agent Scott Boras through 29 contentious days of negotiations, signing Matsuzaka to a contract far closer to their original offer ($8-to $9-million a year for six years) than Boras’ original demand ($15- to $16-million a year for three years). And they did it while consciously bending their approach to the Japanese norms of civility and respect. (Matsuzaka, in fact, would say that he decided to sign with the Sox when he realized they would help his family make the cultural adjustments to the United States.)

The immediate result: the signing of a pitcher who, if he approaches the level of excellence he achieved in Japan, could help give the Red Sox one of the best starting rotations in baseball.

“We [want] to make sure to avoid creating too many lofty expectations,” said general manager Theo Epstein, “but Daisuke is unique as a pitcher . . . [He has] quite an arsenal [of pitches], and with the command of his secondary pitches, he’s also an artist and a craftsman on the mound. And he has the character and makeup of a bulldog and a competitor.”

The long-term goal: to give the Red Sox — who earlier this offseason also signed Japanese reliever Hideki Okajima — a chance to tap into the Japanese market, both in terms of talent (regarding players) and revenue (regarding fan interest), in much the same way Pedro Martinez and David Ortiz helped them tap into the Dominican Republic.

The interest is already percolating.

“Theo and I were negotiating [earlier this week],” said Boras, “and I went back to my office at 4:30 in the morning. And in my parking lot, at 4:30 in the morning, were 70 reporters waiting for an update on Daisuke. So I assure you that . . . he’s certainly someone who is, if not the [biggest], then one of the biggest attractions [I’ve ever represented].”

Lucchino — addressing what he called “the new Japanese members of Red Sox Nation” — attempted immediately to capitalize on that interest.

“We recognize that Daisuke is, as he’s been described, a national treasure,” said Lucchino. “Well, we have a national treasure here, as well. It’s called Fenway Park. We invite, warmly, the members of the Japanese baseball world to come to visit Fenway Park, to visit Boston, to visit the great New England region. We look forward to their participation in Red Sox Nation.”

Matsuzaka’s interpreter’s command of the English language was shaky, and thus the pitcher’s translated comments were brief and, occasionally, unintelligible. About the only clear statement related by the interpreter was when Matsuzaka said, “I’m very happy and excited to be a member of the Boston Red Sox.”

No more happy and excited than the Red Sox are to have him.

“This,” said Henry, “is a joyous day in New England.”