Still In S.h.a.p.e.? Postmark Query

I was sorting through some old Belgian postcards and came across this postmark from 1989 on a card from Mons, Belgium. Unaware of what S.H.A.P.E. is I "googled" it and discovered it is an anacronym for " Strategic Headquarters Allied Powers Europe", part of NATO. It has been operating since 1951, but since 2003 has been controlling all operations worldwide.
Does anyone know anything about the post office there - what services it offers and examples of other types of postmark?