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Justice Sonia Sotomayor referred to it as "a vulgar word with relationship to selling clothes," a reference to the Los Angeles-based fashion brand by the same name, seeking to qualify for U.S. trademark protection.
Chief Justice John Roberts called it the "vulgar word at the heart of the case." Justice Stephen Breyer called it a word "used to insult somebody, rather like fighting words."
"FUCT" -- which founder Erik Brunetti says is pronounced by saying each letter -- was denied a trademark because the government deemed it "scandalous" and "immoral."
The question before the court: Whether words like "FUCT" must be eligible for trademark registration because of First Amendment protection of free speech or whether there's a legitimate public interest in keeping the government disassociated from profane language.
The justices wrestled openly with the dilemma, showing some concern that federal law prohibiting registration of trademarks that are "scandalous" or "immoral" is too subjective, inconsistently enforced and potentially discriminatory.
"What about [the] argument that the use of the word expresses a viewpoint precisely because of its offensiveness? You know, it's edgy, it expresses a non-conformist attitude, all of that?" Roberts asked of Deputy Solicitor General Malcom Stewart, who was defending the trademark law.
"One way or another, it's always subjective," Sotomayor said.
The government argued that it wasn't taking a position on the speech itself but rather the "mode of expression," invoking a public interest in limiting exposure to profanity among children and others who find it hurtful.
Justice Samuel Alito came to the administration's defense when he said, "The government is not saying, you can't use this phrase, this word, [but just that] we won't register it."
Breyer suggested denying a trademark to "FUCT" did little to suppress speech. "What exactly is the harm to the First Amendment speech interest here?" he said. "I mean, this is, after all, simply not forbidding use of any word in any place, but you can't put a little R next to it."
John Sommer, the attorney representing "FUCT" and its founder, argued that the government was, in fact, discriminating against a certain type of speech in denying a government benefit.
"They have a viewpoint that they want to make," Sommer said of the fashion line. "Brunetti cannot express his viewpoint without an unconstitutional burden."
Several justices acknowledged Sommer's claim that the current standard has been inconsistently applied. For example, the terms "FCUK," "THE F WORD," and "F'D" were all approved for trademarks while "F U," "EFFU" and "FVCKED" were not.
"There are shocking numbers of ones granted and ones refused" that "do look remarkably similar," said Justice Neil Gorsuch.
In 2017, the Supreme Court struck down a similar part of the federal trademark law -- one which had banned trademark registration for "disparaging" language. The justices said, in a unanimous opinion, that "giving offense is a viewpoint" protected by the First Amendment.
The court is expected to deliver an opinion in the case by the end of June.