A siglum (plural sigla) is a letter (or other character) used to designate any number of the following: a witness or a group (or a family) of witnesses, a vertex/node in a graph, or the archetype and hyparchetypes in a textual or manuscript tradition.
Often editors will distinguish witnesses from hyparchetypes by employing Roman letters for the former and Greek letters for the latter (see, for example, Fig. 1 under archetype). However, editorial practice can vary – Barber's edition of Propertius (1953), uses Greek letters for three witnesses from the fifteenth century.
A number of additional conventions also exist. For example, a lower case f with a superscript letter (fª) can be used to denote a witness preserved as a fragment as in the manuscript sigla for Ælfric's homilies established by Godden (1979) and Clemoes (1997). Additionally, lower- and upper-case Roman letters may be employed to distinguish witnesses based on their date as in Mynors' edition of Vergil (1969); manuscripts from the fourth and fifth centuries have upper-case sigla while those from the end of the eighth century and the ninth century are represented by lower-case letters. A number or a letter in superscript next to the siglum of a manuscript may also indicate another hand or another layer within the manuscript. For example, if M is the siglum of a manuscript, M1 or Ma may indicate that another hand corrected the manuscript at some point, and, in cases where further campaigns of correction may be identified, further sigla such as M2 or Mb etc. can be used. The same conventions can also be used to characterize composite manuscripts, in which two or more codicological units from different periods can be identified. The prime symbol is often used as well in such cases; for example, M is a manuscript copied in the 12th century, the text was incomplete and has been added later on the last pages of the same manuscript, this later addition is called M'.
Usually a table of sigla under such headings as 'manuscript sigla', 'sigla codicum', 'conspectus siglorum', or simply 'sigla' is found preceding the text of the edition. See also abbreviations and editorial signs.
– Barber, Eric Arthur, ed. 1953. Sexti Properti Carmina. Oxford Classical Texts. Oxford: Oxford University Press.
– Clemoes, Peter, ed. 1997. Ælfric's Catholic Homilies: The First Series. Early English Text Society, Supplementary Series, vol. 17. Oxford: Oxford University Press.
– Godden, Malcolm, ed. 1979. Ælfric's Catholic Homilies: The Second Series. Early English Text Society, Supplementary Series, vol. 5. London: Oxford University Press.
– Mynors, Roger A.B., ed. 1969. P. Vergili Maronis Opera. Oxford Classical Texts. Oxford: Oxford University Press.