This topic dangles precariously over the vast abyss known as "Disneyland micro-trivia," but in the end it escapes, Indiana Jones style, and lands squarely in the midst of the historical narration of the Haunted Mansion's development, where it plays a small but significant role. That's significant in the most literal possible reading of the word.
Our subject today is this pre-opening sign:
I think it's the best "coming attraction" sign they've ever done, but then I'm obviously biased.
The official story runs something like this: Shortly after the façade building—that handsome white mansion—was completed in early 1963, Marty Sklar wrote up the text for this sign, and it was placed outside the gate of the HM. There it hung for six years, since the ride did not open until 1969. It actually played a role in establishing the basic concept for the ride after years of conflict and indecision among competing ideas advanced by various Imagineers as to what sort of attraction the HM ought to be. There was a period of sheer neglect at WED (= WDI) while other projects occupied everyone's attention (chiefly Pirates of the Caribbean and the New York World's Fair), but when the HM project was resumed, so was the controversy about the basic premise of the ride. At the end of the day it was decided that the Mansion should indeed be presented as a retirement home for a motley collection of ghosts, just like Sklar's sign had been telling people since the day the building went up. That's the story, and you find it reflected in whole or in part in many authoritative sources, including Marty Sklar's Foreward to Jason Surrell's Haunted Mansion book (p. 6).
The sign was featured in a publicity photo that has itself become a collector's item:
And Now for the Inevitable Historical Revisionism
There have always been problems with the 1963 date. The text refers to the "Museum of the Supernatural," which was another name for the "Museum of the Weird," which was Walt's idea for how to use Rolly Crump's surrealistic creations for the Mansion, as most of you know. That particular brainstorm took place in the fall of 1964, according to Rolly. Another problem is that photos taken in 1964 do not show the sign.