This was made by a group of Cambuur Ultra's. The Anti-Boer tag on the side is a reference to the fooballclub SC Heerenveen. Who the Cambuur supporters call farmers, since they don't live in a city. The SC Heerenveen supporters immediately painted white and blue paint over it, but that was removed pretty quickly. 
You can find this work on the top of the St. Stephansonsviaduct.