Marco Cimarosti scripsit:

> It does actually also have that utilitarian function of avoiding
> modification of the text, but that's also true of, e.g., the diagonal line
> often seen on Western digit zero, or the crossbar seen on digit seven:

As I understand it, these are for disambiguation rather than security:
0 vs. O, 7 vs 1 (in styles where 1 has an upper serif but no lower serif).
North Americans, as you probably know, write 1 as a simple vertical line
and do not cross 7.

> Perhaps, automatically adding such signs could be a feature of a
> "science-fiction-level" OpenType font.

We hope!

Here lies the Christian, John Cowan
judge, and poet Peter,
Who broke the laws of God
and man and metre. cowan@...