My Machzor Rabba, nusach Ashkenaz, sometimes prints a dot, and sometimes an א at the bottom of the page. Anyone know why?
I've included pictures of a double page with two dots, one with two alephs, and one with one of each.
You find this a lot in older Sefarim. Usually you can find these in the margin closest to the binding - often hidden in the binding.
It seems that this was how they differentiate between versions. Like between Pessach, Sukkoth and Shavuoth Machzorim, which use plenty common pages.
In the case of the Machzor Rabba, they really used the same text for both version - but switched some critical pages for Nussach Ashkenaz.
Since the Ashkenaz and Sefard machzorim are so similar, they put an א in the margin for the Ashkenaz-specific pages.
If you pay close attention you can find places in the Ashkenaz machzor that are clearly Nussach Sefard. Occasionally you'll find a "dual Nussach" like the וְיַצְמַח פֻּרְקָנֵה, וִיקָרֵב מְשִׁיחֵהּ put in parentheses. This saves them from having to double-print too many pages.
So the Ashkenaz-specific pages are identified, to help the binding process. (In Israel, the printer and the binder are usually separate businesses.)