According to the tv series "Evil" - people can't read in their dreams.

The next night, however, Kristen foils the demon, who has introduced himself as George. She tapes a sign on the ceiling above her bed, and, after George slices off one of her fingers, she stares up. "I can't read it!" she says in relief—he's only a night terror, since, she explains, Wernicke's area, the part of the brain that interprets language, is dormant during sleep. "Well, if I don't exist, then this won't hurt," George says, raising his knife and stabbing her in the heart, as she wakes up gasping.

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Related - Blue checks are bad wherever they are. - Hexbear