When running up a project containing the 10.2.7 version of the ArcGis maps, in my App.xaml.cs I set the ArcGISRuntimeEnvironment.ClientId property to a 16 character string that I got when I went through the account creating process. This removes the development watermark from the map as expected. However, if I change the client id to be ANY random cocktail of 16 characters it has the same affect, it will remove the watermark and work.
Why doesn't it matter what ID I put in? If it's being used as part of an offline system, how is it even authenticated?