It’s probably too late now to say sorry, Justin Bieber.

San Francisco’s city attorney Dennis Herrera sent a letter to the pop singer’s record label, Def Jam Recordings, requesting full cooperation to find and punish those who spray-painted ads that promote Mr. Bieber’s latest album, “Purpose.”

The ads, which the city has observed to be part of a guerrilla marketing tactic, have sprung up in various San Francisco neighborhoods starting mid-December. According to a statement from the city attorney’s office, the public works department has been responding to a string of complaints about the stenciled ads, which have yet to fade despite rain.

The stenciled prints mostly say, "Justin Bieber Purpose #Nov. 13" in a white, scrawled font, and at least eight photos of the ads were sent as evidence along with the letter to the record label. The paint seems to be permanent.

“Far more infuriating to the San Franciscans I hear from is commercially-sponsored graffiti vandalism,” Mr. Herrera wrote to Def Jam chief executive officer Steve Bartels and Universal Music general counsel and executive vice president Jeffrey Harleston. "As city attorney, I take the illegal graffiti marketed for Mr. Bieber’s album seriously, and I will aggressively pursue all available penalties and costs from those responsible for lawless marketing tactics that intend to financially benefit your respective companies.”

Def Jam Recording faces potential civil litigation from the city, court-ordered injunctions, and fines of up to $2,500 for each violation. Matt Dorsey, Herrera’s spokesman and an admitted Bieber fan, said he isn’t certain how much it would cost to clean up the graffiti.

"These are visual distractions for pedestrian safety," Mr. Dorsey told NBC on Monday, standing near one of the implicated Bieber ad. "And it sends a message to young people, 'Hey, if Justin Bieber does this, it's OK for you to do it.'"

According to the city attorney’s office, the Bieber campaign is the worst case of vandalism as part of a guerrilla marketing campaign, a tactic that has been popularized recently.

It isn’t the first time San Francisco has dealt with illegal marketing. In 2001 and 2004, IBM and NBCUniversal, respectively, spray painted their logos throughout the city as part of a similar ad campaign. Their ad agencies ended up paying the city $103,000 and $100,000, Dorsey said. And when video game company Zynga's advertising company cluttered sidewalks with stickers, Dorsey said the company paid $45,000 in cleanup fees.

“Graffiti abatement and prevention are important aspects of protecting the quality of life in San Francisco neighborhoods,” city supervisor Aaron Peskin said in a statement. He is currently working on legislation that would heighten penalties for cases such as this.

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“Unfortunately, current penalties for ‘guerrilla marketing’ graffiti seem to reflect an acceptable cost of doing business by irresponsible companies competing for consumers’ attention," he added. "It’s clear that we need to enact tougher penalties to more effectively discourage this practice.”

The “Sorry” singer himself has yet to comment, and no one has stepped forward to take responsibility for the spray paint campaign.