The shirts, which would read "What happens at Derby stays at Derby," are too close for the comfort of tourism boosters who zealously guard the popular, and protected, "What happens here, stays here" slogan.

But the most recent dispute prompted discussion among tourism officials, who are fighting at least six similar battles over the slogan, about whether some trademark protection victories are worth the cost of the fight.

"This is not going to be the last of these," said Oscar Goodman, mayor of Las Vegas and chairman of the convention authority's board of directors, of the Derby application. "If it doesn't hurt us, I'm not sure we want to spend the money to stop it."

Legal wrangling over trademarked Las Vegas phrases in the six cases, including one in which the authority is a defendant, have cost $732,123 to date.

At issue Tuesday was a May 2006 application by Michaelle Latas-Wisniewski of Chicago to the U.S. Patent and Trademark Office. The application seeks to trademark the phrase "What happens at Derby Stays at Derby!" for use on hats, T-shirts and novelty buttons, according to a filing by Latas-Wisniewski.

Neither Latas-Wisniewski nor the attorney listed on the application returned a call for comment.

Luke Puschnig, the visitors authority's legal counsel, said the Derby phrase infringes on the tourism group's trademarked phrase, which is attributed with helping to make Las Vegas one of country's the most recognized brands.

"We believe it will create confusion in the marketplace," Puschnig told the authority board.

The Las Vegas phrase made its debut in 2002 and since then more than $131 million has been spent marketing it as a catchy slogan to attract visitors to Southern Nevada, where tourism is a nearly $40 billion annual industry.

But protecting the phrases hasn't been cheap.

A dispute with a California woman, scheduled to go before a judge in Reno April 18, has already cost the authority $623,283.

Last year a judge stopped the woman, Dorothy Tovar of Placerville, Calif., in her attempt to use the phrase "What happens in Vegas, stays in Vegas," on souvenir clothing, including underwear.

"I don't want to be monitoring underwear for the next several years," Goodman said.

The court date next week in Reno is regarding whether Tovar will owe the authority damages over the dispute. The cost of the legal fight rankled authority members who took umbrage with Tovar's use of the phrase and the costly battle.

"Put to a vote, I wouldn't give her a cent," Goodman said.

In another recent dispute, the authority voted to challenge a trademark application by a software company seeking to use the phrase "Only in Vegas," for a video game. The authority argued the video game title would infringe on its trademarked phrase, "Only Vegas."

Puschnig said ignoring trademark applications, even if they seem benign, could be dangerous.

That's because inaction in one case could be used against the authority in future cases, which could dilute the value of trademarked phrase, Puschnig said.

"If we don't fight this one, our argument to dispute dilution may be compromised," he said.