No you shouldn't give those people negative trust.
It's allowed on this forum to create topics about the ponzi. If you don't want to have users promoting it, you should first stop the topics about the ponzi. If you allowed to first, you should accept the second.
Creating a topic about ponzi is different from advertising or promoting ponzi
When we create a topic about ponzi, that is a way for us to discuss what the site is all about.
Topics like this helps educate and warn others that site is ponzi
Unlike a signature, it will say something about the site but not definitely say that site is pozi
A topic is also promotion for the ponzi. Its just made to get people to the website. You're right about the signature doesnt mention its a ponzi, but people can read right. If you see something like 'GET YOUR BTC DOUBLES WITHIN 24 HOURS' there should go some alarm-bells ringing.