Wiktionary
heavy metal umlaut
n. An umlaut over a letter in the name of a heavy metal band (as in "http://en.wikipedia.org/wiki/Mot%C3%B6rhead", "http://en.wikipedia.org/wiki/Queensr%C3%BFche" and "http://en.wikipedia.org/wiki/M%C3%B6tley%20Cr%C3%BCe"), added gratuitously for mere stylistic effect.