The heading is clear: "Found a brown diary". Did you lose one?
The location is clear: Do you live in Berlin?
If the answer is "no" to the above questions - what the hell are you doing reading the thread?
Thankfully we've got a TT member from Karlsruhe to maintain the integrity of the Berlin section.
Just last week NYCLabretts found a cell phone in a metro station
with English texts so he posted here that he found it, and he was basically called a dumbass by numerous people for not turning it in to the metro authority. That is an item where once he removed it from the spot he could still find the owner.
People are just giving common sense advice on this thread, which shouldn't have to be region-specific. Turn it in! But, the person who lost it has most likely retraced their steps and since no one turned it in they will never be reunited with their brown-covered book which may or may not contain English. A tragic end to a blossoming relationship based on one's innermost secrets.