Vandals struck Loyola Academy in Wilmette sometime over the weekend.
Crews were seen Monday morning clearing off an offensive message that had been scrawled on the press box at Sachs Stadium, the school's soccer and football field.
Another message was discovered on the sidewalks near the football field.
The act may be a senior prank by students at another school. One of the messages appeared to read "New Trier Seniors."
NBC Chicago has reached out to school officials for comment.