Electronic Arts MUS

Electronic Arts MUS files were used, in several variants, in some Electronic Arts games in the 1989-92 period, including Cartooners (which was actually an animated-cartoon creator rather than a game, per se), Ski or Die, The Lost Files of Sherlock Holmes, and (apparently in a very different format, perhaps compressed) The Immortal.

Identification
The signature bytes at the start of the file are  for the Cartooners version, and   in other versions.

Links

 * Article on Video Game Music Preservation Foundation Wiki
 * Some format info (zipped text file)