Any Evidence of Riots in Germany?

 NO.  ZERO.

I probably read of a dozen social media types trying to suggest the riots had 'arrived'.....but all BS.

Preventative measures?  If you were a German student on some agenda with violence....the police will detain you....call the parents, and start measures over them.  

Also, you'd be playing into the hands of the AfD Party....suggesting that the CDU-CSU-SPD coalition were 'weak' on crime.