4. No referral code (ref link) spam.
The word Spam which I bolded gave the rule number 4 a totally different meaning from what you might perceive it as.
If means when making post members are not allowed to spam the forum with referral codes or links but does mean you can't post a refer link when it's needed. You just don't spam it, link posting on every board with the link or code, for people to use it for your benefit like it is done in the good old days where refer is the most common task earn bitcoin or rewards.
If you post link to source of information without giving a description to it, it's meaningless as Mia Chloe may say that it's not informative and other members of the forum can't communicate to it because they wouldn't know your point if the post isn't explained by poster. Also as extracting informations from a source without providing its link or referral codes is spamming because it's likely that you're disguising to make the post with your own ability while the essence of the reference source link and your inputs justifies it not spamming.