I've been based in Berlin for almost two years now. That's a long enough period to become receptive to certain changes in the environment. I consider them as "weak signals".

• Teenagers' week-end invasions. Yes, especially at the Schönhauser corner. The Finnish slang has words pissis or fruittari, respectively for a boy and a girl. The closest German word I know would be die Tussi. In London, I suppose they're known as Essex girls and chavs.
• Broken glass on streets. There's more now than during the World Cup. Might be related to the first signal.
• Begging children. Usually they're foreigners, some might play an instrument. This is a very heartbreaking development.

They all sound a tad negative, don't they? I had one positive weak signal in my mind, but I forgot it. Maybe later.

I first became aware of the "weak signals" via Elina Hiltunen's eponymous blog (although I haven't been following it since it moved). According to her weak signals mean "strange things that exist today and that can tell about big trends in the future".