I am fairly confident that it was because you were wearing a paid signature and were making insubstantial posts. Looking at the last 3 pages of your post history I see that you have made pretty much nothing more then one liners and slightly longer, but still insubstantial posts.

You can try to appeal your ban to get it to expire early, however you will need to give a good reason why this should happen. I personally have not seen anyone ever post/give a good reason why their ban should expire early.