"Detectability of Extraterrestrial Technological Activities" by Guillermo A. Lemarchand:
http://www.coseti.org/lemarch1.htm
Dr. Allen Tough proposes that ETI are here in the form of interstellar nanoprobes and are monitoring our Internet. This may explain why they haven't contacted us. :^)
http://members.aol.com/WelcomeETI/7.html
And for an idea of what finding an alien civilization on Mars might be like:
http://www.challenger.org/gallery/mars/images/C_TheKey3.jpg
Larry
