I'm not sure when this label was added, but it looks to me like something the prop room may have taped on.
The cup (and the rest of Tina's props) come with a certificate which I believe Tina created.
Hurley is very pleased with the cup, but a little perplexed as to how it grew to so large a size.
Here are some screencaps where the cup can be seen:
This is the clearest shot of Hurley's cup.