What are the technical symbols used in the margin of a page called?
Solution 1:
I would call those additions marginalia:
notes in the margin of a book, manuscript, or letter
[C19: New Latin, noun (neuter plural) from marginālis, 'marginal']
As for a suitable verb, try annotate.
Solution 2:
Postil {Postiling} or {Postilling}.] To write postils, or marginal notes; to comment; to postillate. [1913 Webster]
Apostille or Apostil n. deriv. of apostiller to add marginal notes, postilla marginal note
Scholium A marginal annotation; an explanatory remark or comment; specifically, an explanatory comment on the text of a classic author by an early grammarian. [1913 Webster]
- A remark or observation subjoined to a demonstration or a train of reasoning. [1913 Webster]
If you are looking for a key to read the symbols. or google "ecclesiastical logograms"