Federal investigators are looking into multiple reports of vandalism on Southwest Airlines planes.
Arabic or Arabic-like symbols are showing up written in dirt and soot on the outside of planes, according to the FBI.
"This has been going on for several months," Southwest spokesperson Brandy King said in a statement. "We continue to track the impacted fleet, logging when and where the vandalism is taking place."
King declined to give specific details, including which airports were affected.
Southwest Airlines sent out an internal memo saying the markings will be handled as an "internal vandalism issue."