Currently signature campaigns are not standardized, and therefore a signature campaign manager can dictate their own rules as long as they're abiding by the forum guidelines. 

Meta is for forum related issues yeah, but this is more related to signature campaigns entry criteria, and would probably be more suited to Service Discussion because its exactly that discussion about signature campaigns rather than the forum. You're not suggesting a change to the forums guidelines, but you're suggesting that campaign managers change their criteria of accepting certain types of users. A common misconception is Signature campaigns are related to the forum, when really they only exist on the forum.