The Los Angeles Times said the Playboy founder gave $900,000, while the Tiffany & Co.
Foundation and Aileen Getty donated $500,000 to the cause.
The trust now has the $12.5 million it needs to buy Cahuenga Peak, the 138-acre site where the iconic sign sits, from Fox River Financial Resources Inc., which reportedly planned to build luxury homes there.
The property once belonged to late aviator and filmmaker Howard Hughes.
"It's like saying let's build a house in the middle of Yellowstone Park," Hefner told the Times. "There are some things that are more important. The Hollywood sign represents the dreams of millions. It's a symbol. It is as the Eiffel Tower is to Paris. It represents the movies."