There is no such a rule, unless it is spam or phishing.
You should know this as you have been longer here than me, try to avoid making false statements which are not helpful at all.
https://bitcointalk.org/index.php?topic=703657.04. No referral code (ref link) spam. [1]
As far as I can tell the interpretation of spam here is generally that you should not post any referral links. The punishment seems harsh though, I think mostly the posts just get deleted unless someone keeps doing it.