A lot of old recipe books have a section at the back featuring something like miscellaneous tips and tricks, and I found the following in a book from 1912, when cars would have still been unusual:

A ten-cent megaphone is a most useful article to carry on motor trips. It enables one to ask directions of people some distance away and makes one's "Thank you" audible to the kind informant one has already passed.

HEY YOU! CAN YOU DIRECT ME TO ROUTE 12? THANK YOU!

Source: The Book of a Thousand Recipes, Arranged for The River Forest Women’s Club. River Forest, Illinois, 1912