January 1974 Doubleday Publisher's Letter. Sorry, I don't have the original so can't scan for better resolution. Part of the description of this letter (from Heritage Auctions Lot 45328 10/8/2014) states that the signature is a facsimile:
" .... original publisher's promotional typed letter sent to bookstores, dated January, 1974 on Doubleday stationery, in which the publisher (William G. Thompson, who signs with a facsimile signature), states that: "We feel that it may be the novel of the year - a headlong narrative with the drive and relentless power of THE EXORCIST, with the high voltage shock of ROSEMARY'S BABY." In a later paragraph (in a fit of understatement), he writes: "We think CARRIE and Stephen King have a bright future..."