Since there was no issue available in the new currency (those stamps only became available on July 3 with the mechanical overprint issue Mi183-197) and one could not be created quickly, it was decreed that all available Pfennig value stamps of the second Control Commission issue on hand in the post offices should be overprinted with a district stamp and sold for the new currency”
They were valid only from 24th June to 10th July, (although some sources suggest also “first post” on 11th July), in any part of the Soviet Zone. They were also valid for this period in West Berlin.
See: “ The Russians in Germany Stamps 1945-49 (Soviet Zone)”
https://www.stampboards.com/viewtopic.php?f=17&t=16899
for much more on these district hand stamped issues.
Here is a typical example:

SBZ Mi173I Bezirk:3 (Berlin- Grünau 1)
It should be noted that many unauthorised overprints were made at the time and many later fakes exist. By collecting ordinary covers with these issues on it seemed more likely that these would be genuine stamps! (Although faked covers do of course exist, they tend to be of higher value ones).
*However the Western Authorities decided to introduce the Deutsche Mark in West Berlin.
Example of “Berlin” banknote:
Also: for an example of the Soviet Zone “emergency” notes see:
“The bank note with a stamp! 1948 East German "Kupon" note”
https://www.stampboards.com/viewtopic.php?f=17&t=54725&p=3821608#p3821608
I decided to form a collection of covers which would include every day of validity and every Bezirk (District). There are 10 District numbers (plus a variation of District 29) and 17 days of validity. (Obviously not every Bezirk on every day- this would need 187 covers!) It also includes a few extras such as out of validity covers (postage due- “nachgebühr”).
Each district includes a number of towns (there is some overlap) and in the case of Berlin, districts of the city. Including different colours and fonts there are around 2530 different possible overprints and taking into account different stamp values around 30000 different possible combinations!
Later I started a collection (not mutually exclusive) based on a map of the Soviet Zone. This is currently incomplete due to other interests but I will show what I have after the above one.