Does it matter which hand is on top?
Generally, no. You can place whichever hand feels most comfortable on top. However, many people naturally place their non-dominant hand higher near the mouth and their dominant hand lower, just as they might hold a real saxophone.
How is this different from signing clarinet or flute?
While all three involve wiggling fingers, the hand placement changes. For a flute, both hands are held out to the side. For a clarinet, the hands are held straight down in front of the mouth. For a saxophone, the hands are angled slightly outward and down, mimicking its distinct curved shape.
Do I need to puff my cheeks while signing saxophone?
You don't have to puff your cheeks, but adding a slight facial expression or mouth movement that mimics blowing into the mouthpiece can make your sign look much more natural, expressive, and clear.