The signature of an increased greenhouse effect is a hot spot about 10km up in the atmosphere over the tropics. We have been measuring the atmosphere for decades using radiosondes: weather balloons with thermometers that radio back the temperature as the balloon ascends through the atmosphere. They show no hot spot. Whatsoever.
The way I look at it, the whole issue in global warming is to find the smoking gun, so to speak, that links carbon dioxide to global warming. This "greenhouse signature" sounds like it would have been a real smoking gun.
Of course, one can argue that by the time we find the smoking gun it may be too late. Perhaps in the meantime we'd better play it safe and act as if the global warming thesis is true. That would not be my position, though.
UPDATE: In the comments, Tim Lambert writes,
The signature of an increased greenhouse effect is not a hot spot 10km up. That effect is a predicted consequence of surface warming, whether from greenhouse or the sun.
The signature of greenhouse warming is stratospheric cooling. Which is what we're seeing. Which is why Evans doesn't mention it.
More Denialism, from dissident and peer-disdained physicists, here and here