Front and back of three postcards sent by Cascadia Artpost (the USA). The first two show catalogues of artistamps creators, and samples of their word.
The title of this postcard is Famous Postmarks. There is the explanation on the back:
The retirement of long-time artist C.T. Chew from mail art at the end of 2017 had the effect of immediately rendering his "Aesthetics" postmark ant other Triangle Post telematic ephemera as scarce trace phenomena in the postalscape of the Eternal Network. Cascadia Artpost now commemorates the cliquishly referential and unforgettable presence of Chew the mail artist in six memorable images, conveniently portrayed in the artistamp format. All forever hail Triangle Post!