Sheet music became commonplace in homes starting about 1840. Postcards came along some years later, but when the songwriters put their pens to a score postcards and music were a perfect match.
Storefront postcards would seem to be the bailiwick of a local views collector, but as a separate topic within the linen genre of cards there are some very interesting architectural, social, cultural, and even some biographical elements of stories that may never be told. Every card in the essay suggests a question, like “Who was Aunt Jennie?”