We probably need to be on the lookout for this kind of behavior actually. As more and more spammers get banned and restart with newbie accounts, some may resort to this tactic when the realize they will struggle to get that one elusive merit.
It's not a big deal, at least not for now. You don't have to be on a lookout for this at all. If you see a random user putting such signatures on every post, just report him, and mods will take care of it; rather than coming to meta and creating a thread about this new 'threat' and make users go on a wtichhunt for these ad-spamming dumb fuckers,emphasis on the users(which is everyone but bots and LoyceV, obviously).
Maybe there's something else they can do, if they want:
They can quickly archive the post with archive.is and include that short url into the report, just in case the newbie start to edit the post and remove the signature part to escape the ban...