Someone "tagged" the 26-foot-tall statue with graffiti.
They also spray painted a pillar outside a nearby building.
Several surveillance cameras in the area are being checked to see if the person, or persons can be identified.
The sculpture, called "Forever Marilyn," shows the screen icon striking a legendary pose from her 1955 film "The Seven Year Itch."
It’s so tall; you can look up her skirt. Some call it art, others call it gross.
The statue was unveiled in July 2011 and will be removed on May 7, said the the non-profit group that owns the statue.