Well, I have the full set, and all but one of them is signed by the cast.
I tried to make the characters match the drink names:
Morena (Inara) signed Love Potion
Summer (River) signed Self Defence
Alan (Wash) signed Chill Out (because Wash is chilled.. okay, I started stretching at this point!)
Jewel (Kaylee) signed Wake Up (just because)
Nathan (Mal) signed De-Tox (again, just for no real reason!)
You can see the edge of a green bottle behind - that one is called Sharpen Up and is currently unsigned, but that one's for Adam to sign. Because Jayne likes sharp things. Like knives.
And there's a new one just released called Health Kick, which I think Sean Maher will need to sign - because health.. doctor... ahem.
I'll be leaving now!