This is also considered in Keith Houston's entertaining book Shady Characters: The Secret Life of Punctuation, Symbols, and Other Typographical Marks.
It traces the history of some other common symbols such as the at sign and asterisk.
It traces the history of some other common symbols such as the at sign and asterisk.
"Why did so many readers, until relatively recently, take the trouble to stop and draw a whole hand when they simply wanted to mark something as important? And why did so many authors and printers use the increasingly heavy-handed image of the manicule to direct the attention of their readers?" William H. Sherman explains in his 2005 paper, Toward a History of the Manicule [2].
[1] http://hdl.handle.net/2027/uc1.b4200870
[2] http://www.livesandletters.ac.uk/papers/FOR_2005_04_001.pdf