Is few-word/one-liner responses spam?
I voted "It depends".
Posts like "thanks, I appreciate", "interesting topic", "pm me", etc could be regarded as spam depending on the context.
While,
Posts like "run a node instead", "do CPFP", "multiSig wallet is the solution", etc could be short, yet quality.
So you're saying your signature campaign manager encourages spam by setting a minimum post length. There's a better solution:
4. There is no minimum length to make a post constructive, but you can expect scrutiny. If you can post a constructive post in 12 words, you don't need to make it longer.
If I were a signature campaign manager, I would take enough time to recruit quality posters, when I get the right posters to hire, I will remove post length rule.
I understand that the post length rule was introduced because of spammers, I don't think that such rule is strictly applied to everyone.