This is a French acronym used by some mailing list members; it stands for “Exemple Complet Minimal”, or “Complete Minimal Example”. The term refers to test files that can reliably reproduce a bug with the minimal amount of code.
Formatting your signature for news posts
If you like, read RFC 3676:
There is a long-standing convention in Usenet news
which also commonly appears in Internet mail of
using “– ” as the separator line between the body
and the signature of a message.