A New York City police union has put its members on alert after a group known as the Ten Black Guerilla Family threatened to kill on-duty police officers in response to a grand jury’s decision last week not to indict a white police officer in the chokehold death of a black man on Staten Island, according to the New York Daily News. The gang may be targeting police officers in Baltimore, not New York City, according to the Staten Island Advance.

The Ten Black Guerilla Family was formed in the infamous San Quentin State Prison in California in 1966 by George Jackson, a member of the Black Panthers, according to Police magazine. The gang has since spread to the streets of Los Angeles and on the East Coast, including Baltimore, according to the Daily News.

The gang’s goals are “ending racism and overthrowing the U.S. government,” according to police. Ten Black Guerilla Family members usually sport a “BGF” tattoo in gothic text with a rifle crossed with a bloody sword. Some members also wear “276” tattoos, with each number representing the corresponding letters of the alphabet in “BGF.”

The Ten Black Guerilla Family has killed NYPD officers before. Officers Rocco Laurie and Gregory Foster were killed by members of the group in 1972, the Advance noted.

An undercover cop learned of the Ten Black Guerilla Family threat on Friday, two days after NYPD Officer Daniel Pantaleo was not indicted by a grand jury in the chokehold death of Eric Garner. Protests erupted in the city and beyond in response to the decision. The Sergeants Benevolent Association, a police union, disseminated the threat to its members.

“Please wear your vests and carry your firearm off duty along with additional magazines,” SBA President Ed Mullins said in a memo, according to the Daily News. “Your priority is to go home at the end of your tour!”

The NYPD does not believe the threat is targeting its officers, the department’s information arm said in a statement, according to the Advance. "The threat information referenced in a recent news story relates to another East Coast city and does not make reference to New York City or its police,” the statement said. “While we are aware of the information, it is not deemed to be a credible, specific threat to NYPD personnel. We continue to monitor and investigate any threat information as it surfaces. We will continue to advise all members of the service of any credible information relating to officer safety."

An NYPD source told the paper that Baltimore is the city likely being targeted by the Ten Black Guerilla Family, in part because of language in the threat. The threatening letter mentioned killing members of the “Homicide Section,” and the NYPD calls its homicide units squads. Baltimore’s police departments calls its units sections.