In fairness to Tokyo, perhaps they thought the PIRATE! sign might drum up some interest along with the movie changes. The ride just seems perpetually unloved out there compared to the others.
I remember the original WDW Pirate sign. So much classier.
I'm not sure of the exact year but that's roughly when it happened, yes.
EDIT: It was definitely in place by 1993. I think I actually prefer the black sign over the one shown in this picture. At the very least the color of the lettering on this one seems off to me:
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