Gaining trademark protection is substantially more cumbersome and expensive than obtaining copyright registration. Unfortunately, it is also very important if your artwork has a consistent name (such as Dilbert or Wolverine) or character which serves to identify the art. Most artists will do best by familiarizing themselves with the following material, and then seeing a lawyer who is familiar with trademarks (not your local divorce lawyer, since this is a highly specialized field).
The resources on the Basic page will teach you what a trademark is, how to register it, and a little about how to protect it. Every artist needs to know these trademark law basics.
The resources on this page cover some of the more common complications or questions that arise under trademark law. Also, the page addresses specific trademark issues that arise in certain fields of art and writing.
This page is only interesting if you are a lawyer or have a particularly difficult question (or have a morbid curiosity of legal details).