There will still be users and marketing campaigns for sure, however, they will turn into older practices. For instance, bumping, fake reviews, and spamming links services.
If only signature campaigns are removed, but users still can bear a private signature, some will still post to promote their own sites.
That said, removing signature capabilities altogether will demolish any incentive to post -> less traffic -> less valuable domain name.
Signature space is a good way to monetize our own content, i.e., posts and threads. Removing it will make us generate content for free, and I believe many people here don't want to spend enough effort for free, so the spam count will be higher/post quality will be reduced IMO.
There would also be scums trying to still post futile random loan request in the Lending section as well as just creating new services in the Service section even if they were already got tagged before (tag evading). I feel like bounties removal would significantly reduce more of the traffic rather than the SCs alone although I can see SCs still in Bounties, but considering we're seeing a lot of POA posts from people, surely that would affect more.
I also agree with your "signature space" point there. Users are forgetting that signature in our profile pertain on whatever we're trying to show to other users just like those email signatures that we see.
The case is different for signatures under bounties and altcoins because the manager doesn't usually remove participants for underperforming or even look at the number of merits earned. Some managers actually warn their participants regarding post quality, but it doesn't give them enough reason to remove them. Which makes the participants continue doing their sh*t posting, provided that they count it.
Yeah, they just count the posts of their participants into stakes from my experience like 3 years ago. This is why it's kinda worse in the Bounties section rather than the Services section. I am not saying that all are really bad posters in the Bounties section and all good posters are in the Services section though. There are just way many users posting in Bounties rather than in Services section.