Wausau police tell News Channel 7 they believe the crime happened overnight.
Officers say there is some indication the graffiti may be gang-related. A symbol similar to a Jewish star with the number six in the center appears more than once amidst the messages.
Students who came to see the damage say they can't believe it happened to their school.
"I didn't really expect somebody to do that to the school 'cuz it's really hard to clean up," said sophomore Beth Gering.
"Pretty mean whoever did it to do it to a school," commented senior Mark Hadley. "Pretty worthless on their part to get whatever they're trying to get across."
Wausau police say school officials have been told about the graffiti and are making plans to remove it.