Gov. Arnold Schwarzenegger said Monday that Hefner was the final donor, calling it "the Hollywood ending we hoped for."
Hefner's gift caps a yearlong effort by conservationists to keep developers out of the area behind the sign. Aileen Getty, a billionaire daughter of oil baron J. Paul Getty, and The Tiffany and Co. Foundation earlier contributed $1 million.
In a statement, Hefner says the sign is "Hollywood's Eiffel Tower."