Coming to the topic, whats Ognasty's 1/2 BTC suggestion by the way? Didn't have the time to go through the whole thread, but it seems well accepted.
tl;dr pay 2
BTC to get a special rank that can have a signature, everyone else either has super stripped down signature or none.
I would think "Supporters" who paid 2 BTC would get: a signature, new title, new "who's online" color, access to the Donators section of the forum, and having your name listed here:
https://bitcointalk.org/donate.htmlBAN SIGNATURES FOR FORUM MEMBERS WHO HAVE NOT DONATED TO THE FORUM.
Create a new level of donator called the "Supporter" that can be reached with a 2 BTC donation to bitcointalk.
Only Supporters, Donators, & VIPs are then allowed to have signatures. Perhaps with each level carrying different restrictions.