You don't score SEO points on just text. It has to be an active and valid link. Fresh in the pants spammers might think they're hot shot in plunking down an URL in that field, but it's just text. 

If you want to help them get nowhere, just flag their posts as the spam it already is. The URL in their profile isn't even linked until they have [15 reputation](https://meta.stackexchange.com/questions/105218/is-spam-in-the-about-me-field-a-reason-to-worry "or right on it").