The ‘flower-powered’ ad was designed by Paul Funken (1932–), who was responsible for many of the progressive Swiss-style NMBS advertisements and posters in the 1960s. Arjan den Boer posted a tweet about this poster (translated from Dutch):
The Belgian railways were progressive in poster design in the 1960s. This is mainly thanks to the designers Paul Funken and André Pasture. They developed a Belgian variant of the Swiss Style with sleek typography, lots of white space, and abstracted or geometric representations.