SpamAssassin Rule: SUBJ_RE_NUM
Standard description: Subject is faking 'The Bat!' responses
The Subject line in the mail's header looks like "Subject: Re: something". This is an unusual use of "Re" in the subject line, but it is apparently a signature of 'The Bat!'.
The default scores for this rule can be found in the online list of tests.
Advice on the use of "Re:" is in RFC 2822 sec 3.6.5