Even signatures are not shown there, does it mean spams allowed?
Nope, and on every board, spam is not allowed either.
I only quote very first topics shown on top of Serious discussion board but if you look to more other threads, they are mostly spam.
Is Serious discussion board becomes a spam board and no moderation like in bounties board?
Have you ever tried to "Report to Moderator" ? What's the result ? I think boards like these are mostly faster to be taken care, just see the rules (mentioned a broken english on the rules of those boards). As long as the report explanations are very straight to the point. Perhaps Report: [Serious Discussion] straight-to-the-point reason of your report. Feels too tested.
Diversifying boards and topics in which they post, just to avoid signature ban?
Increasing account activity point?
Trying to fish merit if possible?
Diversifying the posts on every board is not gonna save them either. Nutildah is using a few points, not just their history post before sending the ban. The only things they're gaining on those boards are "potential-activity period". They could try to fish some merit too, but mostly merit sources or other people are really not having so much activity on those boards. Unless there is some discussion, it is quite important for them.
Cheating campaign managers if they don't notice carefully when counting posts in campaigns for payment?
Then, the campaign managers are not doing their jobs correctly.
