Card 12 recognizes Dead Letter Offices. DLOs are unique in that, quite early on, women could work at them. Once source I read states that women were desirable employees because they were more trustworthy than men (and a lot of money was sent via US mail). Other sources say that women were employed by DLOs particularly during the Civil War because men were need to fight. Maybe both are true. What do I know? Whatever you believe, you should learn about Vinnie Ream who was one of the first women to work in a DLO and so much more.
On a side note, the Dead Letter Office died in 1990. RIP Dead Letter Office.