I had many responses to my query about the Hebrew acronym Yod-`ayin-aleph on
the seal of the Jewish Council of Deputies for Bamberg. Many thanks to all.
I pass on the gist of the responses because the same question may arise with
other Hebrew or Yiddish documents or artifacts.
Yod-`ayin-aleph is a customary abbreviation after the name of a locale. In
this context, it is said to represent over a dozen variant phrases, all of
which say in effect: "May God protect our city," or "God make our city
prosper." I don't know the original phrase and I would guess it's been
forgotten. The acronym is still used widely, and all but one of the phrases
given are likely just back formations >from the established abbreviation whose
precise words are now forgotten.