From Sir Arthur Conan Doyle's story "A Case of Identity" from Adventures of Sherlock Holmes, in which Sherlock is quickly closing in on his weasel of a suspect:
'It is a curious thing,' remarked Holmes, 'that a typewriter has really quite as much individuality as a man's handwriting. Unless they are quite new, no two of them write exactly alike. Some letters get more worn than others, and some wear only on one side. Now, you remark in this note of yours, Mr. Windibank, that in every case there is some little slurring over of the "e," and a slight defect in the tail of the "r." There are fourteen other characteristics, but those are the most obvious.'