WikiLeaks Stamp
Stamp(ij)
Although Dutch Authorities of TNT have there rules
Answer on this question:

TNT_Detail_Persoonlijke_Postzegel_Postzegelblog_WikiLeaks
Lezen: PostzegelBlog
There really is such a stamp and it is actually used:
Letter with Stamp (WikiLeaks)

Dutch TNT does have limitations for “personal stamps”:
