Disable Spotlight on a FAT32 Drive

sudo mdutil -i off /Volumes/"drive name"/

(quotes around drive name if there are special characters or spaces) then

sudo mdutil -E /Volumes/"drive name"/

via
macosxhints.com – 10.4: Disable Spotlight on a FAT32 external drive
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Read through most of the useful comments, and the original post, to learn the secrets of .metadata_never_index