Created by medieval scribes, that symbol was reproduced by early printers. The presence of the pointing hand in many early sets of lead type justifies Houston’s decision to treat it as a form of standard punctuation. Web-browser programmers adapted or reinvented it for designating hyperlinks as one moves a computer cursor over that part of the screen.
But what’s the standard term for the pointing hand? Houston uses the Latinate word “manicule,” which carries an air of antiquity. However, Michael Quinion reports in World Wide Words:
The history of manicule in English is a bit of a mystery. It isn’t recorded in the recent review of the letter M in the Oxford English Dictionary, nor is it in any other dictionary I’ve been able to consult. And I’ve found no example in print before 1996. However, William Sherman wrote in a detailed study of the sign in 2005 that he had been told it had become the standard term among scholars who study ancient manuscripts. I wonder if his informant actually had manicula in mind, either the Latin word or the identical Italian one; this has certainly been used in English-language works on manuscripts. Alteration of the final letter to turn it into an English equivalent seems to have happened very recently.William H. Sherman’s essay was titled “Toward a History of the Manicule” (PDF download), and it became part of his 2009 book Used Books: Marking Readers in Renaissance England. Sherman noted a host of terms for the symbol:
I have now found 15 other names for what I prefer to follow the manuscript specialists in calling the manicule: hand, pointing hand, hand director, pointer, digit, fist, mutton fist, bishop’s fist, index, indicationum, indicator, indicule, maniple, and pilcrow. The last three terms are outright mistakes: indicule and maniple are mishearings, misrememberings, or conflations of similar words.(Houston’s book also has a long discussion of the pilcrow, which is this: ¶.)
The official, and long-established, English term for the pointing hand is “index.” However, we use that word for other things in designing books today, so perhaps we should adopt “manicule” and pretend it’s much older than what the evidence points to.