There are some gambling threads here in BitcoinTalk that use invite codes to track their engagement here in BitcoinTalk. I think this is only allowed if you are the representative of that casino. However, I haven't read about this; I've seen many gambling threads doing this even in signature campaign threads with image hyperlinks so I think it is allowed.
I myself have some doubts about ref links in posts, especially in Gambling boards, because I saw that some members of the forum do exactly what is prohibited by the rules of the forum.
In this topic, the global mod explained his position, but in the end it all boils down to the personal opinion of the moderator in the specific case.
newbies cannot wear a signature or Personal Text, you cannot promote referral links, you need to level up or purchase a copper membership.
I didn't know that newbies can't even have a personal text, but I guess that everyone can make a little effort and become a Jr.Member in a very short time.