The fact that a crappy post is allowed in the forum doesn't mean that it is allowed in this specific campaign. There ARE clear rules:
No spam, flaming, single word (or image), short sentence, bump, me too, thanks, other forum(off-topic,meta, Politics & Society, Beginners & Help,Archival) or other obviously crappy posts, - these posts will not be paid.
You've been banned here already; no use arguing it. Find another sig campaign and make better posts, or don't participate in one. I myself am careful to only make good posts as opposed to one-liners and spam, and I haven't had any problems here. Perhaps if you can make good, well-written, well-thought-out, and thorough posts, you may have a chance to be readmitted to this campaign. I wouldn't count on it though.