Trade Cards, or Trading Cards, are 2.5 x 3.5 inches and can be anything you want: cartoon (as above), pencil, markers, painting, mixed-media... there's no limit to what artists are doing. I've seen full on pencil portraits or paintings you wouldn't think are done on something this small.
During comic book conventions artists will often do quick cartoons of various movie and comic characters to sell on the spot, anywhere from $5 to $20 a piece and even up to $50 depending on the artist!
The two above are from a Star Trek series I did where I left it up to the customer to color in however they wished.
Finding the collection reminded me that anything I do at home I scan and sure enough, I have a bunch of these cards on file! Yeah!
Four of the Star Trek cards are in the process of being turned into coloring pages, to be uploaded soon for the $4+ patrons.
Also coming within the next two weeks: more New Mexico watercolor landscapes.
edit 7.22.17 - Coloring pages now ready to download.
edit 10.3.17 - Trading Cards now under "Art Cards ACEO" category.