Officials at a Tennessee social justice center known for training Martin Luther King Jr., Rosa Parks, and over civil rights leaders said in a statement Tuesday that a “white power” symbol was found after its main office was destroyed in a fire last week.

On Friday, the Highlander Research and Education Center, which played a key role in organizing boycotts in Montgomery, Alabama, and founding the Student Nonviolent Coordinating Committee, lost one of the 10 buildings on its rural property in New Market, Tennessee, to a fire. Local law enforcement officers are working with the state bomb and arson agents to investigate the possibility of a targeted attack, according to NBC News. No one was harmed in Friday’s fire.

“While we do not know the names of the culprits, we know that the white power movement has been increasing and consolidating power across the South, across this nation, and globally,” the center said in the statement. “Because of our history we are not surprised that this space, one where marginalized people working across sectors, geographies and identities show up consistently, has been repeatedly targeted over our 87 years of existence.”

A spokeswoman for Highlander told CBS News that the symbol, which was spray-painted on the parking lot outside the building that burned, “looks like a tic-tac-toe board” and is “connected to a well-known white power movement.”

Jefferson County Sheriff Jeff Coffey told the Knoxville News Sentinel that his office asked another law enforcement agency to help identify the symbol and verify its meaning. “It’s not a traditional, throw-it-in-your-face symbol that you would immediately recognize,” he said. “But it has been used by individuals in the past.”

Highlander acknowledged that its location likely meant a “process that takes more time in a rural geography with limited public resources.” According to the center, Friday’s fire destroyed decades’ worth of documents, speeches, memorabilia, and other artifacts from the civil rights movement.