Depending on budget 2-3 Sparkasse branded buses can be provided on weekends or even weekdays for free use for the Berlin citizens and visitors.
These buses go to the main Points of Interest in Berlin.
At each stop (POI) you can hop on and off for "FREE". The cool feature is: On the bus, there is a Sparkasse ATM to withdraw some before arriving next POI.
Thus, the savings bank allows the Berliner citizens and tourists to get from "A to B" or even to make a sightseeing tour for free.
This concept will benefit the people of Berlin as well as the Berlin tourism. Since the buses are rented directly at the Berlin transport companies, no competition caused by this action.