I can't say I'm that sure about the effectiveness of this. Let's take one of the most notorious campaigns for spam as an example, YoBit. A large amount of members removed from that campaign are below 'Member' rank (AFAIK). It is not difficult to get the potential activity for an account to that level, especially if said spammer is managing several accounts at the same time.
Due to this, I don't think that this would be too much of a problem for people dedicated to spamming due to their ability to switch accounts should a negative repercussion happen to one. This would be even less of a problem if the implementation included staged punishments (3 days, 7 days etc) as if one account had their signature removed they could move to another account, then move back once said other account account had their signature removed.