It is illegal to make unauthorized alterations to the sign. Although the city has occasionally allowed it in the past for commercial purposes, current policy does not permit changes to be made. This is largely due to neighborhood opposition and to past accidents. However, the sign has been unofficially altered a number of times, often eliciting a great deal of attention. Some of the more famous modifications have included:

* HOLLYWeeD – January 1976, following the passage of a state law decriminalizing marijuana.
* HOLLYWEED – December 1983, for the opening scene of the film Hollywood Hot Tubs.
* HOLYWOOD – April 1977, for Easter sunrise service, viewable from the Hollywood Bowl.
* GO NAVY – November 1983, before that year's Army–Navy Game at the Rose Bowl stadium.
* RAFFEYSOD – January 1985, reportedly done by a band called "The Raffeys", who were trying to drum up publicity.
* HOLLYWOOD II – April 1986, to mark the revitalization of area.
* FOX – April 1987, for promotion of the television network.
* CALTECH – May 1987
* OLLYWOOD – July 1987, during the Iran-Contra hearings.
* HOLYWOOD – September 1987, for Pope John Paul II's arrival.
* USCWOOD – 1987, for the annual USC-UCLA football game.
* As part of a promotion for the 1992 film Cool World, a 75-foot-tall cutout of Holli Would was installed, appearing to sit on the sign. The alteration angered local residents,[9][10] who picketed the unveiling of the altered sign.[11]
* OIL WAR – 1991, for the Gulf War.
* PEROTWOOD – During the 1992 presidential election, showing support for candidate Ross Perot.
* PINKYWOOD – for the 1992 Don Bluth film Rock-a-Doodle during a chase scene around the "Pinky Pictures" studio back lot.
* GO UCLA – 1993, for the annual UCLA-USC football game. Twenty members of UCLA's Theta Chi fraternity achieved the prank, and were subsequently charged with trespassing. This incident prompted the 1994 installation of a $100,000 security system featuring video surveillance and motion detection.
* PEROTWOOD – During the 1996 presidential election in support of candidate Ross Perot.
* JOLLYGOOD – When Virgin Atlantic began flying nonstop from LA to London.
* On January 1, 2000, the sign was lit up in an array of flashing colors in celebration of the new millennium.
* CALTECH – 2003, on Hollywood's centennial (of its incorporation as a municipality).[12]
* HOLLYWOOD - The Super Bowl XLIII Hulu commercial for promotional reasons.