Then there could be a formula to decide whether or not to remove the signature rights
Remember we do not have a clear definition of spam.
It's not about the system deciding something is spam or not.
It's about the system deciding whether or not a person gets to wear a signature based on their "spam score" "post reputation" (whatever it might be called).
Eg can you wear a signature if 2 (trusted) people marked you as spammer? No, probably. What if 2 people marked you as spammer and 2 marked your posts as good.
Cases like this.
I like the idea of the balance of 2 (or other number) trusted members marking your posts as spam, then the SMAS would kick in and remove the sig block automatically. The balance coming in where if 2 (or other number) trusted members mark your posts as good and then you would go to neutral and your sig block comes active again. The separate spam marker would help with this and it's a "fair" way to mark spammers.