Posting referral links publicly isn't allowed. Sending unsolicited PMs with or without referral links isn't allowed either.
What I suggested is neither spam posting not unsolicited PMs.
Regarding the general rules of the forum, it is not allowed to place ref links in posts - although there are exceptions in the form of someone opening an ANN thread which, if I'm not mistaken, can contain a ref link. Also, a few years ago there were some members who literally spammed the Gambling board with their ref links, but they were apparently allowed to do so - I think I even opened a thread on Meta about it.