Not exactly a postcard, but such signs have recently become a serious collecting sub-genre; rather like those crudely printed 'Money for Food, God Bless' cardboard signs held by homeless people standing on traffic medians or slumped on sidewalks. The Folk Art of Today.
This is an especially heart-wrenching example--15 lb. 'therapy dog' Shih Tzu (with umbilical hernia and missing tooth) has look of transcendental horror. As he must have looked one imagines when man ran off with him--chillingly--'under his arm.'