he's almost entirely correct. i may not be the world's best guitarist but i've sure studied theory :-) he's right, there is no key signature for harmonic minor. you would use the key signature for e natural minor (the same as G major) which has only one sharp: f#. since the harmonic minor scale is a natural minor scale with a raised VII, you would simply put a "#" symbol in front of every D that appears in the song to raise it a half step. that would put the piece in harmonic minor