Okay, this is a game I saw on the DP forums and thought that it looked fun. All you have to do is look at the first person's siggy and say what you think one of the Avatar characters would say if they saw it.
I'll use mine siggy as an example.
Katara: Sokka? A bender? Haha, this girl has her ponytail on a little too tight!
Sokka: Hey! It says Boomerang bender! I can bend a boomerang! (throws boomerang and smirks at Katara) See? (he isn't looking and his boomerang slams into him)
Katara: Yes, oh mighty master bender, whatever you say!
Remember, you're remarking the person in front of you's siggy, not your own.