Are you sure of the reason for the ban? It's my first time that I know participation in signature campaigns causes a ban.
Can you show the ban message?
The main reasons of banned forever are copy/paste without source, Spam, and phishing links.
Next time read sticky rules first.
OP stated the reason: "unsubstantial posts + signature campaign (7 days)"
So yea, most likely posting stuff without much content
(probably useless one-liners) just to gain postcount for OP's campaign that he/she joined. Probably well deserved in my opinion.