Ey up Dave,
The 'R's represent 'Richard Rincker',the manufacturer.
eyes up, Paul, old friend :tinysmile_classes_t
there is a popular error with the double R (in row or back to back) in most discussions here about manufacturer marks.
although Richard Rinker was a very busy company indeed, most early items stamped with RR were n o t made by the Rinker GmbH.
Dave's new fuze RR 189 38 is made by Gebr.Brehmer Maschinenfabrik at Leipzig-Plagwitz (.. 189 ..).
only items with RR & year, RRE etc., RR 336, lwv and (most common) dbk are true Rinker products.
every other combination of RR & two or three digits & year number is not.
for example these two S.Mi.Z.35-boxes (fuze-marks in brackets):
the left one contained Rinker-fuzes from Menden/Iserlohn (RR 1939), the right one pieces made by Hagenuk GmbH, Berlin-Tempelhof (RR 344 38).
this system of nomenclature was introduced in the mid thirties to camouflage the rearmament, as Rinker was one of few 'licensed' manufacturers.
a simple ruse, but still working until today :tinysmile_twink_t2: