As comments in your code you should do the following to tag a group of files as licensed 
under GNU Version 2 License:

1) Add the file GNULICENSE.TXT in your source directory (downloadable where you found this document)

2) For each source file, attach the following as a comment (replacing the stuff within < ...> )

<one line to give the program's name and a brief idea of what it does.>

    Copyright (C) <year>  <your company>  --  <your e-mail address>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA


More general information can be found here:
[ general information at http://www.fsf.org/licensing/licenses/info/GPLv2.html ]