siglum
A letter or other symbol that stands for a name or word; specifically, one used in a modern literary work to refer to an early version of a text.
A thing which represents something else; a sign, a symbol.
figuratively
[H]e emerged onto a garden terrace where on the soft red sand one could make out the sigla of a summer day: the imprints of a dog's paws, the beaded tracks of a wagtail, the Dunlop stripe left by Tanya's bicycle, […]
Where it comes from
Learned borrowing from Late Latin siglum (“abbreviation”), possibly a contracted form of: * sigillum (“figurine, statuette; seal”), from signum (“figure, statue; seal, signet; mark, sign”) (ultimately from Proto-Indo-European *sek- (“to cut, sever; to cut off”) or *sekʷ- (“to follow”)) + -ulum (diminutive suffix); or * singulum, a singular form of singulus (“apiece; every; single”, adjective), ultimately from Proto-Indo-European *sem- (“one; together”). The plural form sigla is a learned borrowing from Late Latin sigla.
Adapted from the Wiktionary entry siglum (CC BY-SA 4.0).