Maybe you're an old pro at ATC's or maybe you're new to the whole concept. A little background for you (courtesy Wikipedia):
Artist Trading Cards are individual art miniatures which pass hand to hand. Some sources have credited M. Vänçi Stirnemann, who began trading sessions in Zurich, Switzerland, in 1997, as popularizing ATCs in the modern era, although modern ATC's can be traced back to portrait miniatures and to a kind of business card popular with Impressionistic era artists.
Artists have produced miniatures for trade or self-promotion in many eras and places, and the current trend is thus part of this larger context. Historically there were few standard rules or guidelines to art trading cards, and many variances in sizes can be seen in older cards. The standardization in size of baseball cards is credited with creating the standardization in size for art cards. Today the only rule for these cards is their 2.5 by 3.5 inch size (64 x 89 mm), same as baseball cards and collectible card games. There are, however, certain conventions usually observed by those who make and trade these cards, such as the expectation that they be traded, not sold, and that they be created as unique works or small limited editions of prints. Artists generally sign and date the back, and may also include a title and contact information. For many, the face-to-face trading session is considered an integral part of the concept, although others find each other via the internet and trade by mail.
Artist Trading Cards are typically made on a base of card stock. However, ATCs have been created on metal, stiffened fabric, plastic, clay, glass, balsa wood, leather, embroidery canvas, acetate, heavy watercolor paper, and many other materials. The art on the cards can be done in any media: textile arts, pencil, watercolor, acrylic, oil, collage, scratch board, mixed media, assemblage, digital art, calligraphy, beadwork, rubber stamps, carved soft block stamps, pen and ink, colored pencil, airbrush, pastels, and many others - anything artists use.
When I did a forum search on ATC, I see that there has definitely been some buzz about them! I'd love have you link any ATC's you've done...I have a feeling that we might be cooking up a little RAK by the end of the week!
Here's a few links that I'd like to share with you, if you're interested in learning more about ATC's!