Apparently he is referring those users who will use the signature code freely without having payment for that. And their intention would be to obtain some referral by using their own affiliate link. I have used my freebitco account affiliate link in my signature here for long time. I was hoping for some active referrals. I noticed visits through my affiliate link everyday but hardly got small number of referrals. Maybe no one will use the signature code for free but anyone can use it while not participating at any campaign.