Relax, it’s just post card collecting. You know, the cards that people mailed from vacation spots, greetings for a special day or just to show off a special interest.
It turns out that this is the 3rd largest collecting hobby after stamps and money. …..Who knew?
Here is a small part of the history according to wikipedia.
“…there are some general rules to dating when a postcard was printed. Postcards are generally sent within a few years of their printing so the postmark helps date a postcard. If the card is original and not a reprint, a postcard’s original printing date can be deduced from such things as the fashions worn by people in the card, the era in which the cars on the street were made, and other time sensitive clues.
Picture postcards (PPCs) can be assigned to “the Golden Age of Postcards” (1898-1918), the time of the linens (circa 1930-1950), or to the modern chromes (after 1940), Modern chromes are color photographs and thus differ from photochromes generated from black and white photographs prior to WWI. PPCs can also be differentiated on the basis of other features: undivided backs are typical for c1901-1906, and divided backs for c1907-1915, while white border cards are common from c1915-1930.”