Rod,
The Shofar (the horn) is used during the Jewish New Year and also on Yom Kippur - the 10th day in the Jewish calendar - in which Jews fast and pray for redemption. The sound of the Shofar is used in the ceremonies as a metaphor for the prayers of the believers and symbolizes the uniqueness of that specific moment in which God listens to their prayers and forgive their sins.
More on WIKI:
http://en.wikipedia.org/wiki/ShofarThe Hebrew inscription on your charity stamp says: "A year of Redemption and Salvation" and also a quote from the Old Testament (Book of Isaiah Chapter 27 verse 13) "...that day , that the great trumpet (in Hebrew: Shofar)shall be blown..."
This quote talks about the future recognition of the empires which conquered the land of Judea and destroyed it in God and explains your cinderella stamps very well.
Obviously it was printed in the USA before the state of Israel was born (It states Jerusalem, Palestine on the inscription and not Jerusalem, Israel as we would write today) and it shows a praying man who asks for salvation. It quotes a biblical verse which talks about recognition of the nations in the Jewish God. All this to say the stamps were printed to reflect the national Jewish sentiment and the longing for a modern independent Jewish state.
I hope - that wasn't too long....