Through the process of trying to find the designer behind this stamp, I discovered the great resource site TNT Post. With the help of Google translate, I think the above design might be a collaboration between Nicolaas Jacobus van de Vecht, S.H. de Roos, and Michiel de Klerk (or just one of them?). The design is the result of a Dutch postage stamp design competition held in 1920.
more stuff to browse here: www.iconenvandepost.nl/
Any expertise/clarity on this appreciated.