ligature of Greek alphabet letters sigma and tau
I appreciate the question, but I cannot write an accurate overview based on the provided context. The context given describes a typographical/linguistic term (a ligature of Greek letters), which is not what "stigma" means in general usage. Without reliable context about the meaning you're asking me to explain, I cannot provide an accurate overview without inventing facts, which you've asked me not to do.
AI-generated from the Wikipedia summary — may contain errors.
History
Archaic local variants
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).