Using the "combining long solidus overlay" Unicode character to draw the
"slashed zero" does not look very good on many systems. It looks fine
on my local machine, with the DejaVu font package that comes with
Fedora, but that's about it. The web font apparently does not have this
character, so browsers fall back to another system font to render it,
which can have varying results.
The DejaVu Sans Mono font has a "dotted" zero, which is similar enough
to a "slashed" zero. Unless you're looking very closely, you can't
really see that the callsign is in a different font, so I think this
works fine.
I really don't want to use the "Latin capital O with slash" character
for this, since that is completely incorrect, but I do want to have the
zero stylized like ham radio operators do.
Dustin