De Beers LV, the retail chain, can stop a New York diamond dealer from selling diamonds under the name “De Beers” on the Internet, a judge ruled recently.

New York diamond dealer Marvin Rosenblatt incorporated the name “DeBeers Diamond Syndicate” in 1981, and eventually let the trademark lapse. In the meantime, De Beers also registered the name, but only had use of it for the general category of “luxury goods.” Rosenblatt soon snagged use of it for the more specific category of “diamonds.” In 2002, court papers say, he applied for and obtained 35 Internet domain names, including variations of the name “De Beers,” such as “debeersdiamonds.biz” and “debeersdiamondswholesale.biz.”

De Beers sued, and after company employees—including De Beers veterans S. Lynn Diamond and Joan Parker—testified to its long-standing use of the name, a judge ruled that Rosenblatt acted in “bad faith,” saying the domain registration was an attempt “to deceive the public and sow confusion.” The judge noted that, in his first trademark registration, “Other than showing that Rosenblatt put the company name on the door of his family business, an action which apparently caused some amusement among the occupants of [his] building, the defendants have not shown through credible evidence that Syndicate engaged in commercial activity.”

Rosenblatt reportedly plans to appeal.

The court papers also included one interesting nugget about De Beers LV’s performance so far: “In the half year in which they were open in 2005, the two American stores had total sales of close to $5 million.”