Actually, for the example we're referring to, neither of us are right. Since both Motley and Crue are not broken apart syllable-wise where the umlaut and/or diaeresis is. There's also no change of the vowel sound in either case, so, as Tony first pointed out, there's no reason for the punctuation. So, in esssense, neither of us are correct. As for what the thing IS, I think the two are interchangeable. The break is to signify that there's a break in the sound from the rest of the word. In this sense, both are accurate, but one is more specific as to when it's used.

Hehe... we're both right AND we're both wrong. LOL! Now, class, in tomorrow's lesson, we'll learn ebonics!

George