Scribal abbreviations, or sigla (singular: siglum), are abbreviations used by ancient and medieval scribes writing in various languages, including Latin, Greek, Old English and Old Norse.
In modern manuscript editing (substantive and mechanical) sigla are the symbols used to indicate the source manuscript (e.g. variations in text between different such manuscripts).
An overline, overscore, or overbar, is a typographical feature of a horizontal line drawn immediately above the text. In old mathematical notation, an overline was called a vinculum, a notation for grouping symbols which is expressed in modern notation by parentheses, though it persists for symbols under a radical sign. The original use in Ancient Greek was to indicate compositions of Greek letters as Greek numerals. In Latin, it indicates Roman numerals multiplied by a thousand and it forms medieval abbreviations (sigla). Marking one or more words with a continuous line above the characters is sometimes called overstriking, though overstriking generally refers to printing one character on top of an already-printed character.
An overline, that is, a single line above a chunk of text, should not be confused with the macron, a diacritical mark placed above (or sometimes below) individual letters. The macron is narrower than the character box.
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