Originally milk needed to be delivered to houses daily as poor refrigeration meant it would quickly spoil. The near-ubiquity of refrigerators in homes in the developed world has decreased the need for frequent milk delivery over the past half-century and made the profession shrink in many localities, and disappear totally in others.
Ok, what is this????
It is a device that allows the customers to signal to the milkman what they want on a specific day.
One day, as a joke, I pulled up all the signals and left it before I went to school. Needless to say Mom was pretty angry when she had garlic ice cream and strawberry butter.