Artist trading cards(or ATCs) are miniature works of art about the same size as modern baseball card (2 ½" X 3 ½") inches. The ATC movement developed out of the mail art movement and has its origins in Switzerland. Cards are produced in various media: pencils, pens, markers, watercolor, acrylic paints, collage, papercuts, found objects or even metals or cloth. The cards are usually traded or exchanged. There are really great web sites dedicated to ATC cards and can give you some great design ideas.
You may be lucky enough to received an activity packet as a promotional item at Glamatria or an art or craft show in Spokane. Here are some examples of the theme's handed out (2012-13).