Place it in the game folder or in the music folder?
Place a copy of .nomedia in whatever folder contains items that you don't want to have appear in the Gallery (for images and videos) or the Music app (for mp3s, wav files, and any other audio files).
Useless Trivia:
.nomedia is similar to a robots.txt file that a web page owner can place in the same directory as the rest of their site to get search engines to ignore the content in their search aggregations.
