Regarding Guy Gardner, I've now decided that Guy's sign name should be linked to his lapels, as that is a very distinctive jacket he's wearing. I do believe no other GL has a uniform quite like it.
How about Power Girl?
It would be the shape of the boob window. No question.
As for her civilian name, a pun on Starr seems easy, so the sign for star then, whilst you lipspeak her first name.
As for the Wonder family. Take Wonder Woman:
Before I said you'd just sign Wonder+Woman. But to make it an actual sign name, you could trace the W shape on your chest and lipspeak either Diana, Wondy, or Wonder Woman.
For Donna Troy:
Again, easy. Do the sign for sparkle all over your torso and lipspeak Donna.
For Wonder Girl (Cassie) I think it would very much depend on her outfit. For an early version of her costume:
Whether she's wearing her blond hair short or she's wearing a wig, the goggles are a mainstay. So let's make the sign for goggles (either on her forehead or her eyes), and lipspeak Wonder Girl or Cassie.
That's all for today's lessons, I'll be back in a few weeks with more!