What can I do with the fine from the police of Berlin that hasn't yet come per Post?

First, sit back and relax. I’ll assume you gave them your correct address (they probably copied it from your ID). It is then on them to contact you in time.

The real question you should be asking yourself is whether the fine will run into limitation issues. Generally speaking, fines that result from Ordnungswidrigkeiten in traffic – and incorrectly crossing the road would be one of those – have a limitation period of three months. This period can be interrupted once by

• questioning the suspect
• creating the Bußgeldbescheid (the document requesting you to pay); or
• delivering the Bußgeldbescheid

If the period is interrupted, a second three month limitation period begins. If the period is interrupted a second time, nothing happens.

The way you describe it, you were probably interrogated in some form on-site. That means, the limitation might have already been interrupted and you’re on your second three-month period. (This obviously would not apply if, say, you ran into a speed camera as a camera has no interrogation options.) These lawyers’ web pages suggest that this issue should always be investigated if the authority attempts to reset the period by requesting an interrogation by mail or the likes.

Once the three-month period has run down, you’re good, they have no more leverage over you. Until the three months run down, just wait patiently for the letter in the mail, keeping your fingers crossed that they may have forgotten about you. Never wake up the sleeping dogs!