Call me biased as I am wearing one, but I don't think a paid signature is really the problem. I see (new) members spamming low quality posts without the use of signatures ...
Account farming. It's a thing.
Paid signatures do incentivize spam/low quality posting, but I don't believe that they are the overall root of the problem.
Nothing is the root of
all evil, we have to settle for making things better piecemeal, symptomatically even.
Paid signatures don't disincentivize spam/low quality posting, so let's get rid of them & make this forum a [slightly] better place.
Then we can keep making it better, one step at a time.