Holmes deduces that the person who wrote the note did not want his or her handwriting to be recognized, and was in a hurry.
In The Hound of the Baskervilles, a mysterious spectral dog has been stalking the Baskerville family for generations. When another Baskerville dies, famous private detective Sherlock Holmes is called to the case to try to save the last Baskerville, who is returning to his ancestral home.
Before he returns home, Baskerville stops at a hotel. He tells no one he is there, but he receives a note warning him that it is not safe to return home.
Holmes makes several deductions from the warning note. The name “was printed in rough characters” and the postmark was Charring Cross the day before (ch 4, p. 23).
Since no one knew where Baskerville would be, Holmes deduces that someone is “very deeply interested” in his movements (ch 4, p. 23).
The words are mostly cut from newspapers, “by the expedient of pasting printed words,” but one word is hand-written: “moor” (p. 23). From this Holmes deduces that the writer of the note could not find that word in the newspaper. Holmes knows not only what newspaper the words are cut from, but the exact articles.
Holmes also realizes that the words were cut with nail scissors, “very short-bladed scissors” (p. 25) and pasted with gum. Holmes can also tell some things about the person who wrote the note.
We may take it, therefore, that the letter was composed by an educated man who wished to pose as an uneducated one, and his effort to conceal his own writing suggests that that writing might be known, or come to be known, by you. (p. 25)
Since the words are uneven, he knows that the writer faced “agitation and hurry,” and the “address has been written in an hotel.” He can tell this because the pen and ink are of bad quality.