That kind of posts happens when a signature campaign requires x amount of post in the gambling section whereas these users don't even know what gambling is, posting nonsense just for the requirements.
So if you don't know what to post in the gambling section, just don't participate in signature campaigns that requires it.
When the majority of signature campaigns require posts in the same specific section, people will post in that section just to be seen as someone who frequently posts in that section to get chosen for the campaign.
The only way to address this problem is to put pressure on campaign managers to not require posts in specific sections.