disabling or filtering sig ads can reduce post spammers yes, but it will decrease helpful post too even a little.. but for me, maybe the option to filter sig ads can only be enabled and disable based on the forum rank of the user.. the higher the rank the more option/s they will have 
What is the need for 'rank' in disabling/enabling/filtering? Forum is allowing everyone to enable/disable signatures, avatars and ads and also to ignore. So this is option should also be available for everyone regardless of the rank.
It depends of which is (will be) the forum policy, if they want to allow a decentralized ad "system" or limit the possibility of what someone can put in their signature. I think this forum is so full of freedom, and I hope they will not "ban" at all the signature campaign. However the feature (if it will be implemented) should be granted to all the forum ranks and not only to the high ranker ( for example full, senior, etc..).
I know they will do the right thing, for fight & stop the spammers (who make insubstantial posts).