When download the packages in Visual Studio there are two version of the same packages for ServiceStack.
ServiceStack ServiceStack Signed
What is the difference?
ServiceStack NuGet packages with a .Signed Suffix are strong-named, where other ServiceStack packages are not Strong named by default except for ServiceStack.Interfaces which is both Strong-Named and a pure PCL library for maximum accessibility.
The ServiceStack download page maintains the list of available Signed packages.