gnus-supercite-regexp

gnus-supercite-regexp is a variable defined in `gnus-cite.el'.
Its value is

"^\\(\\([ 	]*\\(\\w\\|[_.]\\)+>+\\|[ 	]*[]>|]\\)+\\)? *>>>>> +\"\\([^\"\n]+\\)\" +=="

Documentation:
*Regexp matching normal Supercite attribution lines.
The first grouping must match prefixes added by other packages.

You can customize this variable.