As a Ba'al Kri'ah (Torah reader), I sometimes find it difficult to locate the start of an aliyah (reading) on Shabbat, esp. in parshiot Vayetze and Miketz where both of these are one contiguous parsha (paragraph) with no breaks.
Would one be allowed (before Shabbat, of course) to mark in the side margin where the aliyot are located?
I've see sofrim sometimes mark in pencil something in the margin that indicates the place for a correction or some serial number that they need for their records (I guess when scanning). So, I'm uncertain if there is an exception for sofrim in certain occasions and, whether only an erasable marking may be used (like an erasable marker or pencil) or may one use a permanent marker as well?