While the form of the letters of the top row of the siegelmarke are essentially illegible, I believe the characters are "countable" as a pattern of 3 characters, space, 8 characters. If the three characters are AMT it is logical that a location would follow
My Google search locates an image of an "Amt Niedermarsberg" siegelmarke pasted below. Also pasted below is a copy of page 50 of Stefani Konstanti's "Die Region Sauerland unde ihre Dastellung in Museum" which notes association of Marsberg and Kreis Brilon as highlighted in yellow.
THE BIG QUESTION IS: TO WHICH POLICE FORCE DID THIS SIEGELMARKE RELATE AND THEREFORE MIGHT THE HOLSTER AND P.H.W. KURT REUTER HAVE BELONGED IN THE ESTIMATED 1926-1928 TIMEFRAME?
Previously: 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 _ _ _" (sütterlinschrift "Ü")
4th line: "Dienstgebrauch _ _ _" (sütterlinschrift "Ü")
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 _ _"