I feel like the current copyright headers are getting very unwieldy, especially in files that change often (e.g. C4Game.cpp, C4Landscape.cpp, CMakeLists.txt, etc.).

I therefore propose a different header as follows:

/*
 * OpenClonk, http://www.openclonk.org
 *
 * Copyright (c) 2001-2009, RedWolf Design GmbH, http://www.clonk.de/¹
 * Copyright (c) 2009-<YEAR>, The OpenClonk Team and contributors²
 *
 * Distributed under the terms of the ISC license; see accompanying file
 * "COPYING" for details.
 *
 * "Clonk" is a registered trademark of Matthes Bender, used with permission.
 * See accompanying file "TRADEMARK" for details.
 *
 * To redistribute this file outside of OpenClonk, substitute the full
 * license texts for the above references.
 */

The contributor list and ISC license text will then be merged into a single file "COPYING" (name up for debate). I believe this does not require separate permission by all authors because the copyright notice stays in all copies of the software, just as the license requires.

¹ Where applicable; leave out in files written in their entirety after OpenClonk was first published.
² Replace starting year as appropriate.