It's quite an important event when players start to not worry about experience points any more and concentrate on simply playing the roles of their characters. We suggest marking the occasion with some form of ceremony.

Wearing black seems appropriate.

Transcript

GM: Speaking of being nice to people: Obi-Wan, you've abandoned Anakin to his fate and have returned to the landing platform.
Obi-Wan: I couldn't deny Anakin's dying wish.
Anakin: Ben, I'm so pleased you noticed my progression along the path to the Dark Side.
Obi-Wan: Well, of course. You set it up so well.
Obi-Wan: So did you two collude on that Padmé choking thing?
Anakin: No, Jim totally surprised me there.
R2-D2: Wow Jim, that's the first time I've ever seen you actually paying attention to what's happened in the story.
GM: Yes, I've awarded 3000 XP for roleplaying.
R2-D2: Cool. Looks like your corpse is going to level up.
GM: Actually, Padmé is still alive. Barely. C-3PO has moved her unconscious body into the ship.
C-3PO: Goodness me, seeing her lying there just made me shudder!
Padmé: The XP are nice and all, but you know... I don't need them to roleplay.
{beat}
R2-D2: It's like the end of an era.