When a preposition is followed by a sentence, then add da-. However
ein Zeichen von Diabetes becomes
ein Zeichen dass er Diabetes hat
without davon. What is special about Zeichen and what are other such special cases?!
ein Zeichen von Diabetes
ein Zeichen der Diabetes
ein Zeichen (davon), dass er Diabetes hat
The davon is optional, it's actually good style not to use it here. That is because genitive attributes are preferred over von-objects in German, and this extends to object clauses that replace them, too.
So this is a feature of von. Or better, a way to avoid the von.
Man sieht es am anderen Verhalten der anderen Präpositionen.
Man sieht es daran, dass die anderen Präpositionen sich anders verhalten.
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Please elaborate on ""genitive attributes are preferred over von-objects". In which situations? Is "von" frowned at these constructions? – Beta Apr 9 '18 at 8:36
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The preposition von marks the origin of something. This can be used in the sense of a place, and in a transferred sense. This latter use is 100% covered by genitive attributes already and they should be used instead. In sentences with many genitives, von is used instead of a genitive to denote the owner: Dies ist ein Zeichen der Diabetes des Patienten von Dr. Boess. – Janka Apr 9 '18 at 8:53
