The repro is blank back while the original has the balfour stamp (that is what I have concluded from the research I have just done)
"Balfour did make and distribute reproductions of pins around 1991-1992 with identifying marks which were serially numbered."
Repro "This pin is blank backed and believed to have been made in 1991 by Balfour. The pin is of the same size as the original with a push pin back"
"I believe because of the limited number of pins found and recently distributed that they were either samples or would not be issued by the company without marks identifying them as reproduction."
That being said, one could determine there was a decent amount of reproductions released.
Americanmemorabilia auctioned one off as original it was stamped "Balfour" at the bottom on the back.
I hope this helps!
Berger:
http://www.ebay.com/itm/1959-World-S...item43a0032f04
Repro:
http://www.ebay.com/itm/Reproduction...item53deefa5f7
AM:
http://www.americanmemorabilia.com/A...1919&offset=30