Posted October 28th, 2013 @ 02:30pm by Erik J. Barzeski
Very simply put, you can no longer sign a bundle (like your .app) if any nested bundle in that package is unsigned. These nested bundles are things like helper executables, embedded frameworks, plug-ins and XPC services.
The result is that you'll need to update your Xcode projects as soon as you start building on 10.9. It's taken me several days to understand what these changes are, and with the help of Perry Kiehtreiber on the developer forums, I'd like to share what I've learned.