We have heard from a number of (unnamed) sources close to the band that Rancid has in fact signed to Warner. The first rumours of this reached us about two weeks ago, but because of the lack of independent confirmation, we didn't say anything. Now, after making a lot of phone calls, I can say with relative certainty, that the next Rancid record will be on Warner. We're still waiting for the band's management to confirm as well, but this looks like a done deal. More information to come as we get it.
One other note is that Tim Armstrong's imprint, Hellcat remains with Epitaph.

Update: The band's management has confirmed with Punknews.org that Rancid will indeed be "working with Warner Bros." on the upcoming record; second to that, Billboard has posted an article as well.