Commercial art trading cards are definitely being made already, I don't think we'd be stepping on any toes legally to do so ourselves; however, what I noticed browsing the non sport section is that some of the people used art in the title some did not. If you do a search of an artist like Frazetta or Elvgren in the trading cards section (Frazetta I'm guessing would be in fantasy), they may or may not have art in the title. As far as art trading cards for trading amongst artists, I think those are generally one of a kinds, and while a very wonderful idea as well, I don't see how they could claim a trademark on the name when people have been making commercial art trading cards for many, many years.
I'm not a lawyer, maybe we should ask one, but when I did a search of "art" in the trading card section, this is what came up:
http://search.ebay.com/art_Other-Non-Sports_W0QQcatrefZC6QQcoactionZcompareQQcoentrypageZsearchQQcop...
I probably wouldn't use the nickname ATC since that is very (in my mind) associated with the intended to trade cards though. Lisa R. studioLR