Yours, Etc.: Origins and Uses of 8 Sign-Offs
1590s, "thing for drying wet spots," agent noun from blot (v.). Meaning "bad writer" is from c.1600. Sense of "day book" is from 1670s, and the word was applied early 19c. to rough drafts, scrap books, notebooks, and draft account books. Hence the police jargon sense "arrest record sheet," recorded from 1887.