meh photoshop is expensive as far as i heard. and signature making is just another one way of me just wasting my freetime so right now upgrading is not what im thinking about. although Photoshop is a better program then Gimp.
Gimp in the other hand is free and provides lots of very useful tools to create a signature. but doesn't have the complete set as what photoshop provides...but i never had photoshop so I can't tell you which is really better. but as far as seeing signature tutorials comparing gimp against photoshop, photoshop wins.