Case law

Decisions available here.

Germany
I 20 U 176/11-Enigma (Düsseldorf 24 Apr 2012) (German)

I 20 U 176/11-Enigma (Düsseldorf 24 Apr 2012) (English) - holding that defendant could use the "Enigma" work title for software modified for its hardware platform and configuration as long as the use did not violate generally accepted practices of trademark and commerce, which in the case of open source software means that the essential functions of the defendant's version of the software are identical, plug-ins and/or extensions of third parties remain compatible, and the defendant abides by the conditions of the GPL license.

U 147/09-Luxor (Hamburg 18 Jan 2012) - discussing the difference between titles and trademarks.

Poland
II GSK 1551/11-Der Grüne Punkt - English summary here

II GSK 1646/11-Der Grüne Punkt - English summary here

New Zealand
KOHA Decision of the Commissioner 91, [2013] NZIPOTM 47 - barring registration of KOHA mark by commercial entity on the basis that it would cause confusion with the library's free and open source library management software, but that the use by the library was not a trademark use because the software was not sold and therefore not used in the course of trade.

United States
''Autodesk, Inc. v. Dassault Sys. Solidworks Corp.'', 685 F. Supp. 2d 1023, 1027-28 (N.D. Cal. 2009) - a file name extension is not use as a trademark.

FreecycleSunnyvale v. Freecycle Network, 626 F.3d 509 (9th Cir. 2010) - finding there was a "naked license," and the trademark abandoned, in a loosely-organized management system.

Planetary Motion, Inc. v. Techsplosion, Inc., 261 F.3d 1188 (11th Cir. 2001) - holding that free distribution of GPL software was a trademark use.

Progress Software Corp. v. MySQL AB, 195 F.Supp.2d 328 (D. Mass. 2002) - after agreement was terminated, defendant had to cease using combination trademark that included GPL software name but could state that its product used the MySQL program.

Sega Enterprises Ltd. v. Accolade, Inc., 977 F.2d 1510 (9th Cir. 1993) - holding that an initialization code (four bytes containing "S-E-G-A"), used to unlock a game console and which caused the display of the SEGA trademark on the screen, could be used by competitors even if it meant the trademark was falsely displayed.