(CNN) A Las Vegas billboard was vandalized to read, "Shoot a school kid only $29," early Thursday morning.

The billboard originally read, "Shoot a .50 caliber only $29." It was an advertisement for a local firing range called Battlefield Vegas , which, according to its website, is a business owned and operated by veterans that features a "military-style complex" a block from the Las Vegas Strip, as well as additional "outdoor training areas."

The billboard company, Lamar, said it "immediately removed the billboard at the request of the authorities, and we're cooperating with law enforcement agencies as they investigate further."

A guerrilla artists collective called INDECLINE took responsibility for changing the billboard. A spokesperson for the collective said, "It was time for us to address gun reform and to do something louder than an AR-15."

INDECLINE said it was motivated by the school shooting in Parkland, Florida, that took 17 lives on February 14. Members of the group used vinyl stickers to alter the original advertising and added a line at the bottom reading, "Defend Lives, Reform Laws."

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