A signature, especially on emails or newsgroup postings.
"The new sig focused on renewable energy met every Tuesday to share research and strategies."
Urine.
Initialism of special interest group: a group formed to discuss a particular topic or issue.
"Sig is rarely used in modern American English, but historically referred to an old Germanic sword; however, since it has no common contemporary everyday usage as a standalone noun like "sign," this request cannot be fulfilled with a natural current sentence. If you meant the acronym SIG (Special Interest Group) or a specific proper name, please clarify for an accurate example."
Usage: Use "sig" to refer specifically to the personalized text block appended to email messages or forum posts rather than your handwritten name at the bottom of a letter. This term is informal and should be reserved for digital communication contexts where brevity is valued.
Latin SIG: Initialism of Sylloge Inscriptionum Graecarum. (Collection of Greek Inscriptions)
"Sig was named after his great-grandfather, who believed the old Germanic tradition of calling a child Sig would bring him strength and courage."
A male given name from German Siegfried
The word sig is a clipping of the longer word signature. It entered English as a shortened form to refer specifically to an abbreviated or stylized version of one's name used for signing documents.