E. Turkowski from Antwerp wrote in his article Magen David on stamps, (the Holy Land philatelist, vol III July 1957 p. 738-739):
The philatelic aspect of a thematic collection must… show two headings: on the one hand Israel (and Judaica) on the other non-Jewish items.
To call any part of our collection “shields of David used abroad” could apply only where such items could be part of our “Judaica”. On all others, six pointed stars have no relation to the Magen David, and, so to describe those figuring, say on stamps of Morocco, is definitely misleading.
E. Turkowski Also mentions that the appearance of six pointed stars on Trinidad stamps is explained by the fact that Trinidad is the Spanish word for Trinity. (And the triangles of the six-pointed star represent the Trinity).
Thanks to Dobush who sent me this article.