Yes, I definitely remember Slashdot doing it, but it was more often than just on registration. Here's an article from 2014 about it, which says that it happens on every login and posting a comment: https://soylentnews.org/article.pl?sid=14/04/09/1925245

At the bottom of that post it says the code was added on 2008-04-16 19:07:46 +0000.