I would not be too wordy in the header of your source files; this is just annoying nonsense that hardly anybody ever reads. Why wouldn't you rather put a very short statement which links to the full legal agreement (NDA, whatever), either by referring to the file distributed with the source code, or with a plain HTTP link?
/*
* This file is subject to the terms and conditions defined in
* file 'LICENSE.txt', which is part of this source code package.
*/
You can then ask your lawyer to provide you with a rock solid, legally sound, text which you store in one single place with your source code distribution.