Surveillance video captured on campus showed a suspect in the mask, a black hooded sweatshirt and dark pants climbing a locked gate around 10:30 p.m. on Oct. 30.
The suspect placed stickers with the phrase at random all over the campus.
Authorities said no other damage had been done to the school, and that the suspect acted alone. Police also said no other similar events happened prior to the incident.
Anyone with more information is urged to call the South Pasadena Police Department at (626) 403-7270.