While Sting had to officially sign with WWE as of this past weekened, The Observer is also reporting that his contract is currently being worked on and is nearly finished. Right now, it's being said they are working on the merchandising part of the deal.
As numerous reports have said, Sting is not expected to be used at WrestleMania 30 this year. While plans can always change, WWE will most likely use Sting's debut in WWE to boost up WrestleMania 31 next year in California.