Reference?
4. No referral code (ref link) spam. [1]
I tried this when I was a Newbie, and quickly learned it's not allowed when my posts were deleted. I still have the PMs:
Read June 30, 2015, 09:57:35 PM Deleted Post Bitcoin Forum
Read July 01, 2015, 08:11:10 AM Deleted Post Bitcoin Forum
Read July 01, 2015, 12:49:47 PM Deleted Post Bitcoin Forum
Perhaps we read this differently:
1 Irrelevant or unsolicited messages sent over the Internet, typically to a large number of users, for the purposes of advertising, phishing, spreading malware, etc.
[...]1.1 Unwanted or intrusive advertising on the Internet.
My understanding and reading of the rule is that referral links are not disallowed, but that you cannot go around randomly posting the link when doing so is not relevant.
There might be cases in which a referral link is necessary to answer a question, for example if a website requires a referral to sign up.