It's indeed from Groningen, but not the shown Makers brand of Fa. Gebr.Deelman
He is not mentioned in the K.A.Citroen (VZN) in the Groningen section.
What is mentioned:
The successor of Tjeerd Rekers in Workum (Friesland) and of the Roelfsema brothers seems to have been Douwe de Jong in Groningen (i 1899-1942).
Back to the name-register Waarborg Holland part 3 - Jong Wz.D.de Meester nr: 12689 index-nr: 4176-4325
I already recognized him from his pseudo brands.
He is included in the collection of the "De Groninger Zilverkamer"