Trying to decipher the mystery of what is being communicated inside this 1926-1927 holster (other than "Sauer 7,65" on the 2nd line which is very clear). Here is the sense I make of the handwriting:
 
1st line: "No 123 des  _ _ _   Verz." 

3rd line: "P.A.W.  Reuter  Ku _ _ _" 

4th line: "Dienstgebrauch  _ _ _" 
 
[![handwriting][1]][1]


As for the "Dienstsiegel" (assumed meaning of the ink stamp) I am clueless but have pasted a few Freistaat Preussen examples in the picture below:
 
top: "_ _ _ _ _ _ _ _ _ _ _ _" 

left-bottom: "_ _ _ I S" 

bottom: "_ _ _ L _ _" 
 
 
[![Dienstsiegel][2]][2]


  [1]: https://i.sstatic.net/hwXSH.jpg
  [2]: https://i.sstatic.net/SGqf8.jpg