Should I copyright my notes?
Two misconceptions here:
I need to "copyright" my intellectual property to protect it. - No. Unless you explicitly indicate otherwise, you already automatically get exclusive copyright to your notes. There is no "copyrighting" process like applying for a patent. The common "Copyright 2018" notice serves as a reminder of this, as well as suggesting a relevant entity to contact about getting permission and to pre-empt any arguments in court that "well it didn't say it was copyrighted". The last point is superfluous, since court would not require the copyright notice either way.
Holding exclusive copyright physically prevents people from copying my intellectual property. - No. While unauthorized copying is illegal, the copyright is not a magic incantation. You still have to find unauthorized copiers, ask them to stop, then sue if they refuse.
So your copyright is only as good as the steps you're willing to take to enforce it. Will you spend your free time trying to track down people who copy your notes? Will you pay a lawyer to send letters to everyone who copies the notes without permission? Will you shell out hundreds or thousands in legal fees to sue when they refuse?
I'm guessing you're just hoping a scary sounding warning will discourage people. In this day and age, I doubt many would be discouraged. At best you could contact their institution (if they have one) and put pressure on them that way. But ultimately, what are you trying to protect here? A few students passing around copied notes? So what?
If you're thinking somebody will take the notes and use them to write a textbook and sell it for money, forget it. If they're planning to do that they can easily change your notes slightly and even if you had a case, you would have to waste horrendous amounts of time and money in court. If your notes are so great that they have non-trivial financial value on their own, just publish them yourself. Otherwise, stop worrying and move on with your life.
From your post, it appears that you want to discourage people from plagiarizing the notes (i.e., copying them and passing them as their own), rather than make such plagiarism illegal (which, as @NateEldredge has observed in his comment, may already be the case if you do nothing). If so, the Berne convention is irrelevant. In my experience, the best discouragement is publicly posting the notes online somewhere; this way, if a teacher reuses them without attribution, students will easily find out (and they will notice -- I have seen at least one rant about a professor that mentioned his reuse of other people's notes as evidence for bad teaching here on academia.SE lately).
If you want to ensure that people can legally copy your notes with attribution but not without, then a good option is the CC BY license (or any other CC license more restrictive than that -- but I'd go with CC BY if this is your only issue).
[Comment extended to answer.]