My suggestion is to restrict users below Member rank from posting outside the Bounties sub-board if they are wearing signatures.
How will they wear signatures if they can't access the bounties board.
We have a little bigger issue here, bots spreading malware, bots getting paid 1000$ for bumping ANN threads, and other things.
What you're suggesting here, has been suggested before, but with little tweaks to it. What they have said is, just remove the ability to wear signature for users under Member rank. But theymos wouldn't implement it, there are legitimate reasons to wear a signature:
I'm using the maximum length for a Newbie signature, and I wouldn't want to lose it.
As much as I hate spam, restricting legit users isn't the right solution. I'd like to see spam banned faster, especially the army of useless "great project" posters in the altcoin section.