I always seem have difficulty determining whether a song is in a major scale, or the relative minor. (the 3rd note back into it, but minor)
Lets use the Pokemon theme song for example. As I remember, it starts on G, and ends on G (vocals start on D, but the synths start on G) (I don't know the chords.)
So this makes me think it could be in G minor, however, it doesn't seem very sad, and it also seems to revolve around the Bb note a lot, so it could be Bb major, which is the equivalent major scale to G minor.
But still because it starts and ends on G, I'm leaning more toward G minor. Maybe switches to Bb major for the chorus. But that's just a guess.
All I have are guesses based on the emotion of the song, and I'd like to have a more concrete idea on how to figure out key signatures.
Yahoo Answers is completely useless on questions like this.