A recent news item in Nature describes detection of methane in the Martian atmosphere. Methane is expected to have a short half-life on Mars, which means that something is actively making the methane-- either some kind of vulcanism, or, possibly, life. Now, as noted planetology journal The Straight Dope has pointed out, cows are a big source of the methane here on earth.
The next scientific effort will be to detect ethane, which is most consistent with living things, but I suggest going straight for the big prize. Where there's beef, there's a McDonald's. I suggest a Very Large Array (VLA) of six year-olds, which should be able to detect the Golden Arches, and therefore evidence of advanced civilization, at distances of up to several light years. They additionally could discern the play area, thus giving vital clues as to the Martians' means of locomotion.