[leephillips]

You can also look at the referrers in your webserver logs. It’s just that someone has to click on the link for it to appear in your logs. And you can discover referrer spam!

[account42]

Browsers are not guaranteed to send Referer headers and some choose not to (or send fake ones) due to the privacy implications.

[leephillips]

Good point. But, in the absence of any other solution, there is at least some data there, sitting in the log files.