I beg to differ, I believe it's more of the spamming than shady business, have you seen the statistics of the increase of posts (which most are spam) after the introduction of the signature? If I can recall clearly I read somewhere (tried retracing but can't find it) that yobit or any project are always welcome to advertise on the forum as far they don't or make their participants to break any forum rules (believing that statement was made by theymos himself)
Committing spam or encouraging others to spam is likely same. Yobit applied this strategy with their participants to spread their name on forum massively. As a result participants started to run after high payments by doing big number of posts which was actually nothing but spamming. We can't put whole blame only on yobit where participants didnt feel it necessary to know about guideline of signature campaign. Obviously who have joined their campaign should think about forum rules before starting to make low quality post just for counting.
As a forum member following forum rules and encouraging others to obey is the first responsibility for us. If we just think about earning but don't bother about our community then proper environment of discussion will be a rare thing very soon. Joining signature campaign is not a bad thing but if you get ban for doing a signature then obviously you should be careful to protect your account before joining. Its always a wise decission to join those signature campaigns who are really care about forum and its community.