The flashguard is a replacement part made by the weapons workshop at the large equipment depot in Spandau (Heereszeugamt Spandau). SuWw is the maker marking, HZa Spandau Waffenwerkstatt. I can't make out the year of manufacture, but its 1930 something. The "waffenamt" isn't really a waffenamt, its the acceptance of the depot's internal inspectors. Looks like Su19, with Su obviously meaning Spandau. Army depots typically used the first and last letter of their city in their inspection stamps. Su for HZa Spangau, Mg for HZa Magdeburg, etc.

The depots made a lot of spare parts in house, mostly smaller items (extractors, safeties, screws, etc.) and tools, but sometimes larger stuff like barrels and holsters.

 

I dunno about the paint, but the blued blade indicates this was an issue during the Weimar Republic- and yes, they were in service (often with the Luftwaffe or Polizei) until WWII.

 

Same opinion this is not period paint, done postwar. Should be removed, the bayonet was refurbished in late 30ies, mostly there is 1937 Spandau parts.