I went through list of campaigns and found that only Bitvest, 777coin and 1xbit pay for posts in this board. But as I see, main problem comes from Bitvest & 777coin participants who spam there. Though, maybe there is some altcoin bounties paying for posts there, but I haven't checked it.
But if signatures would be removed there, would it make any difference? What's the difference between Bitvest & 777coin spamming in off-topic and participant who spam in remaining board? Because if signature will be removed from off-topic, they simply will continue spamming in all remaining board.
Easier to moderate with one less board IMHO. Even if the spams get rerouted to other subforums, more members are active to report them, just like plagiarism.