Linda wrote:

What's SETI looking for? Life forms able to communicate with us? Life intelligent enough to communicate with other similar life forms? Life that can communicate with my dog?
How are the various SETI projects defining what they are searching for?

I see this thread is a week old, but I like to insert my two bits here.  SETI, I think, should really be caused SETB or the Search for Extra-terrestrial Behavior.

"Artificial signals" is somewhat nonsensical unless we care to call intelligence as being (itself) artificial.  Rather, SETI is looking for a subset of nature which behaves in ways (a) similar to ourselves and (b) is detectable with the search strategy employed.

So, from a philosophical perspective, SETI is trying to determine whether nature has chosen only this one case study (our own) in which to allow sentient life to emerge.

Nothing "artificial" about our own signals, or those we're trying to detect.