I'm rarely using my signature and just realized that I can have 4 links to threads + 2 external links.
What I noticed is really low spam sites in signatures after implementing the rule. I am happy with the limits I have.
Just a newbie's opinion--it seems fair to me to require payment for more privileges that staff may consider to be "spammy" things that might bog down a site. I don't think two small text links is spam, though. I won't lie, I post in forums to get backlinks for my {hobby} site. But I join forums that I feel I can contribute to and become a part of and enjoy. I think that's a win-win for people. Someone might join initially just wanting to backlink, but as they stay on and post they might find themselves really enjoying it, learning from it and contributing to making it a better board. That's one reason I allow people to "sig" for their sites on my board too as long as they become quality members as well by posting regularly with decent stuff.