There were a lot of screenshots going around that were fake.
You can play as luigi using some gameshark hacks for palette and scaling.
I saw a HUGE cheat for unlocking luigi I tried many times but failed at many times a long time ago due to some simple mistakes, like losing count and such. But when I think about it today, it doesn't seem likely that there would be cheats that span multiple levels and worlds in such a simple game.
I don't believe "star" would correspond to Super Mario Galaxy considering the length in the release dates.
Paper Mario seems more likely, but perhaps "L" doesn't refer to Luigi at all, perhaps it refers to Link. There was a message saying "M is Real" in one of the Zelda games, if I recall correctly. I never saw it myself, only read about it.
Cheers,
-naota
"I used to do a lot of time travelling when I was younger. I called it 'ta-kwee-la' You would drink this potion and wake up 3 days in the future!" - Craig Ferguson