I recently watched a PBS docu on racism and it told of the practice of sending postcards, photographed images of lynching. Aside from the repulsive racism and hatred that provoked the lynching, more horrifying that the postcards were souvenirs that people mailed all over the country. As one Black journalist commented, "They didn't even bother to put them in envelopes, that's how acceptable lynching was."
I never heard the term you wrote about but it, too, is heart-sickening.