According to the Amalgamated Printers' Association (APA), a prop card is best described as a calling card of the Proprietor of a Private Press.

Prop cards were first advocated by J. Ben Lieberman.  According to Lieberman, "The prop card was invented on Leap Day, 1960.  It leaped into use, and by now is cherished not only by personal or hobby printers and private collectors but also by libraries and museums, which use their collections as bibliographical sources, information files for new props seeking samples to learn from, and as visual artifacts of the growing worldwide personal press movement."

Specs:

The card is printed on 80 lb. cover stock (3" x 5") from Paper Access.

The typeface used is Colwell Handletter, ATF foundry type.  The face was designed by Elizabeth Colwell 1n 1916.  It appears in the 1923 ATF specimen book, but is not offered in the 1934 book -- so it seems to have enjoyed a relatively short commercial life.

The image of the paper helicopter is a copper die from Owosso Graphic Arts.