I have seen few signatures campaign manager limiting their accepted participants to particular board in the forum and I believe this is a abuse of a signature campaign participants right, and for sure as long as you as a participant in a signature campaign have made posts in boards where the signatures are displayed it should be considered as an acceptable posts.
Because the manager is the one in contact with the client and the client wants more visibility and generates leads, and the manager knows the boards and the posters who are likely to give the client's banner boost and leads.
This is the reason that not all posters are automatically accepted; they have to show that they are a good candidate for what the manager is looking for in a poster.
If you are not comfortable with rules, then don't be under a campaign; even companies set up rules on their employers.
