Arnold Zwicky recommends as a bit of summer reading the Wikipedia article on hëavy metäl ümlauts. (The meagre information in the corresponding E2 node includes Rollo's assertion that the band Tröjan failed to gain a following in Sweden because their name means 'the sweater' in Swedish, and "no one likes a band named after an article of clothing." Wait a minute—is this the same Sweden that gave the world the Cardigans?)
Anyway, I think the heävÿ mëtal umläut (which is officially deplored by Diaeresis Defense) needs to be seen as part of a larger phenomenon which I will tentatively call "ăţmǿșpĥęřīċ đįǟĉŕȉŧĩçš," or, for the benefit of people with Unicode-deprived browsers and/or a distaste for gratuitous self-referentiality, "atmospheric diacritics." Ordinary diacritics convey information about the sounds represented by the letters to which they are attached; atmospheric diacritics convey extralinguistic or metalinguistic information, such as "we are a badass metal band," or, as in the case of the Viking Kerosen from the Astérix comics, "I am really speaking Danish, not French":
Kerosen & Zoodvinsen
La grande traversée
R. Goscinny & A. Uderzo, 1975