Actually, Leenia, there IS a reason for the 'G'. Another way of getting at it is to click on 'Insert' from the menu bar. This will give you a list of all the possible 'special' things you can insert, along with their keyboard shortcuts. As would happen, 'T' is taken by 'Tempo' and 'S' by 'Special ending' so they just took the 'g' out of 'signature.'

Sounds to me like there may be a problem with your NoteWorthy installation. Have you tried uninstalling and reinstalling? Anyway, my offer of playing with one or two of your MIDI files still stands. And, since I use NW fairly regularly, feel free to PM or email me with any questions you might have about it.