message-signature-separator

message-signature-separator is a variable defined in `message.el'.
Its value is

"^-- $"

Documentation:
Regexp matching the signature separator.
This variable is used to strip off the signature from quoted text
when `message-cite-function' is
`message-cite-original-without-signature'. Most useful values
are "^-- $" (strict) and "^-- *$" (loose; allow missing
whitespace).

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.3 of Emacs.