My understanding of an ATC.
Artist Trading Card.
This is a small piece of art, designed and created by you on a piece of card/paper/fabric that is 64mm x 89mm.
You swap them almost like business cards, but it is more of a fun way to swap art with people.
You can decorate them any way you want to, with any medium/colour/style you like.
You can make original, one of a kind, unique ATC's.
You can make sets of identical ATC's which would be an Edition
You can make sets of themed ATC's which would be a series.
If you google ATC's then you will see so many sites that will give you ideas.
If you have interests and ideas of your own, make your own art.
I like mine to be inspirational, or if I can find out what my swap partner is interested in, I will tailor make ATC's to suit their tastes.
I like to make recycled ATC's and sparkly ATC's. Nearly every ATC I send out has glitter on it somewhere.
I will try and pop some in the post to you to give you some ideas.