On the right is the description of the coin from Barclay Head's Historia Numorum, p. 230. The description shows the Greek inscription ΠΥΡ (Pyr) with a line over it.
What does this line mean, and how should it be encoded for web pages?
When I converted the Historia Numorum to HTML I rendered the line using inline CSS with an 'overline' text decoration:
<span style="text-decoration: overline;">It is also possible to render such text using the Unicode 'combining overline', U+0305. Here are two examples:
- ΠΥΡ (CSS)
- Π̅Υ̅Ρ̅ (combining overlines).
Until recently I thought the overline indicated a monogram, but Bradley Hudson McLean (An Introduction to Greek Epigraphy, p. 56) explains that the line is an 'abbreviation mark' or 'abbreviation sign' indicating that not all letters are present. This convention was used by engravers and also medieval copyists.
McLean also has a short description of ligatures on page 55, and his examples are the same as some two-letter symbols for magistrates that I have been calling 'monograms'. Usually when we think of ligatures today we think of printers combining ff or ffi for legibility but McLean also mentions the Roman practice of putting one letter on the other, called 'compendia'.
An example of a compendia on a coin is the OV-ligature on this coin of Nikopolis ad Istrum, right before the 12 o'clock position. I don't know of a good way to render compendia in HTML.