I think the simple way to take that line is that your promo code shouldn't be a topic starter, or off-topic.
If someone asks, "Does DH offer unlimited domains?" and someone answers, "Sign up with my promo code and find out," then yes, that person is retarded and probably shouldn't be allowed near promo codes without adult supervision. On the other hand, if someone gives a simple, "yes," and happens to have a code in their sig, the new customer just got his answer and a discount. No problem there.
If it's in your sig, and you answer posts the way you would without a sig, then it's either a) not a problem, or b) your post is the problem and you shouldn't be posting, with or without a code. Posts are moderated whether they have a code in them or not.
While people might do "me too" posts to put the code out there, "me too" posts were around long before promo codes. They just didn't get questioned since there wasn't a code. I read other forums where someone says something worth reading, then 20 people follow up with "+1." There aren't even promo codes in those forums, but I still want to shoot myself after about the 15th +1.
If the post isn't a problem, a code in the sig shouldn't be, especially since DH probably didn't create them with the hopes that we wouldn't use them. I heard a rumor that they like money.
Plus, as I mentioned in another thread, the "just getting it out there" part isn't just for promo codes. People can do the same with plain referral links, links to their commercial sites, or links to their personal sites w/promo codes and referral links. This is nothing new, yet for some reason, it's only getting attention when it's a promo code.
A simple ban on sigs will make sure that no one here benefits from answering questions and that new customers will not get a discount on hosting. How can anything that hurts DH sales, costs new customers extra money and takes money away from people using codes/referrals possibly be a bad idea?
Save up to $96 at Dreamhost with the 96DOLLARSOFF promo code.