The Eszett symbol (ß) in German is used after long vowels and diphthongs instead of ss. Most languages that use diacritical marks in the Roman alphabet do so originally as a sort of short hand to replace certain letters. For example, the circumflex accent in French usually replaces an s (bastiment is written bâtiment, maistre is written maître, etc) although with the 1990 orthographic reform, most accented characters in nouns are now gone. In German, the umlaut is often used to replace the letter e. For example, München (the city) can be spelled Muenchen. Same applies to the name Müller which can be spelled Mueller. Interestingly, the German umlaut is always omitted and the e is always used if the word in question is written in all capitals. For example, while it would be customary to write München, instead of writing MÜNCHEN, one would write MUENCHEN.
OK, removing the language teacher hat and putting on the lighting enthusiast hat.