Unknown sign pt. 2

Well ... thanks for your comments on the funny sign guys. Having been to Donauinsel again today I have checked on the solution: it really is an indicator for bumpy street or change of surface. This means the sign is meanly for the rollerbladers!

It's been another great day out there today. I kind of like Donauinsel with all its different places and people.

Tune I listen to while writing these lines: sound of the TV