One quibble, though, is that entering "r=" or "/r=" (with or without quotes) into a Google site-search or the forum's native search just returns results for "R" and that, of course, is totally useless. At least it does so for me.
It really does not matter. OP was explaining the referral link spamming things. In a URL, it could be anything depending on the developer of the site. However, most of the time we see like this:
r= or
ref= etc.
Truth is the variable can be anything.
I suspect you misunderstood me - I was saying that using the search terms "r=" or "/r=" to find posts with referral links does not work because both Google site-search and the forum's search engine act as if you searched for "R" instead. That would be a brilliant way to find ref-link spam, otherwise.