Seth Shostak got me to thinking.
Before NASA's Viking mission, atmospheric scientist, physiologist and inventor Dr. James Lovelock offered his assistance to NASA regarding how to determine if life is present on the surface of Mars or any other planetary body with a significant atmosphere: spectrographic analysis to see if it is chemically reactive. Life, it seems, has a tendency to perturb atmospheres such that chemical disequilibrium occurs.
The idea is that a planet without life on the surface will have an atmosphere in a state of chemical equilibrium (no longer reactive). The opposite will be true for planets harboring life (consider Earth's extremely reactive atmosphere and the ubiquity of life on its surface). This atmospheric entropy gradient is a signature of life.
We know this about Titan with certainty: its atmosphere is not in a state of chemical equilibrium. It is dynamic and chemically reactive.