@mmx..careful while you cut off the lock (would seem to have all the symptoms of STEALING while you do it)! Maybe there is a Bescheinigung required for it?? (hehe)..wonder what it would be called?
There was a segment about bike locks on Galileo (Pro7) sometime in the last week or so - generally they found that most members of the public who observed them perfoming a hidden-camera-filmed forced removal of bike locks didn't say a thing.
I'd have though that taking your bike's purchase receipt with you is probably not a bad idea if you don't want to have too much explaining to do.
Interestingly, they seem to be able to remove any lock with in seconds, except for those really expensive big fat u-shaped locks - about €70 or so. Trouble is, whilst they are really secure, they weigh a lot, I've never seen the logic; spend loads on money on a nice light weight bike, and then weight it all down with a nice fat lock!