spam-report-gmane-regex

spam-report-gmane-regex is a variable defined in `spam-report.el'.
Its value is

nil

Documentation:
Regexp matching Gmane newsgroups, e.g. "^nntp\+.*:gmane\."
If you are using spam.el, consider setting gnus-spam-process-newsgroups
or the gnus-group-spam-exit-processor-report-gmane group/topic parameter
instead.

You can customize this variable.