Do I have to copyright my material?
The answer is no, although you may spend the money. Since the enactment of the copyright law of 1978, whenever you have anything in a fixed form (the legal term), you already have a common law copyright.
If you submit to magazines and books, please don't put the © symbol. It's a shout about you. It means either you're ignorant of the law or you're afraid that professional editors will steal your material. (In my experience, those who seem the most concerned have the least to fear—their writing probably isn't good enough to steal.)
However, if you use the © for any online submission, I can see that as a way to say to the ignorant, "This is copyrighted and if you copy it, you're stealing."
As one of my friends said, "It probably won't deter anyone. Thieves know it's illegal."
For the next 10 blogs, we're going to look at some of the legal tangles with plagiarism.