For those unfamiliar with "Signs & Symbols": Moore's title is a reference to the protagonist's condition, "referential mania," a where "the patient imagines that everything happening around him is a veiled reference to his personality and existence. He excludes real people from the conspiracy, because he considers himself to be so much more intelligent than other men. Phenomenal nature shadows him wherever he goes. Clouds in the staring sky transmit to each other, by means of slow signs, incredibly detailed information regarding him. His in- most thoughts are discussed at nightfall, in manual alphabet, by darkly gesticulating trees."
Moore's opening shadows Nabokov's as well: "For the fourth time in as many years, they were confronted with the problem of what birthday present to take to a young man who was incurably deranged in his mind. Desires he had none. Man-made objects were to him either hives of evil, vibrant with a malignant activity that he alone could perceive, or gross comforts for which no use could be found in his abstract world. After eliminating a number of articles that might offend him or frighten him (anything in the gadget line, for instance, was taboo), his parents chose a dainty and innocent trifle—a basket with ten different fruit jellies in ten little jars."
The full text of Nabokov's version is a available here. See/hear Mary Gaitskill talking about her love of the novel and reading the whole thing, also in the New Yorker.
(Via the Nabokv-L Listserv.)