Reply #22 is almost a year old and still contains a link to some Russian website - it's obvious SEO spam.
The point is to get links pointing to your target website from other websites which already have a good reputation, thus boosting the target website's reputation. So, as long as their links remain, regardless of the state of their profile, it will continue to be a successful tactic. Spammers' profiles need to obliterated, not just disabled and signature removed.
Possible defensive solution: disable setting of signature and website link for members with profiles less than 30 days old, and possibly require a few (valid) posts. Spamming would then require far more dedication than is worth the trouble.