Perhaps though, there is wiggle room to make it manifestly clear, by including a clear reminder when creating a new post (something along the line of what is mentioned in rule 33 + the example, and emphasizing on referencing the source). This has been commented before on multiple occasions, is seemingly easy to do, and shows some good will to trim the number of cases we recurrently see. Nobody would be able to claim ignorance from there on, which is what we often read.
Any kind of welcome message would be better than nothing at all. If it were up to me, I would display a notification whenever brand-new and newbie accounts try to post something. That should inform them about two things: plagiarism and spamming. That notification should be visible for either a set number of days or until they reach Jr. Member rank for example.
Nice suggestion. It may not 100% eliminate Plagiarism but still it will give a message to the one who are ignorant.
By the way do we have any data that newbie are the ones who do Plagiarism or higher members of the forum also do the same mistake also ?