Spijkstaal would be a fair assumption (whether it's true or not is a different story). This photo dates from 1940 and was taken in Amsterdam, the Netherlands. The provincial license plate indication of "GZ" coincides with the province of North Holland in which Amsterdam is located. The Spijkstaal company was established in 1938. Taking these two facts into consideration the "Spijkstaal" assumption is logical until proven wrong ;-)