They used to be, but it's all tendered now; they lost the national contract, but still provide to most provinces and municipalities.
http://vorige.nrc.nl/economie/article1594978.ece
and more here:
https://www.wegenwiki.nl/Nationale_Bewegwijzeringsdienst
(Dutch)
They used to be, but it's all tendered now; they lost the national contract, but still provide to most provinces and municipalities.