Nowicki, I'm not so sure that copywriting a knife would do much good. I have a commercial art background. As far as copywriting a piece of art is concerned, it's pretty much how rlinger explained it. By putting your name on the knife pretty much copywrites it, but it doesn't do much to protect the design. Here's what I mean... I made a knife for my brother. The design of it was "my own". I put my own in quotation marks because of what Nathan said in his post. Other than a new locking mechanism or something of that nature it's almost impossible to come up with a knife design that hasn't been done over the last several thousand years. My design for my brother's knife was a culmination of experiences and influences in my life as well as interests that my brother had at the time. I could never say that my knife designs are not influenced by anyone elses. Anyway, back to my brothers knife... I sent it to someone to have a sheath made for it. The sheath maker is the wife of a knife maker. Guess what happened... "My" design got two little tweeks and voila, it became a new design for this prominent knife maker. That's the thing with copyrights, they only protect against exact duplication, like a print of an original oil painting for example. For the most part, any minor change makes the copy a "new design". You're better off spending your energy establishing yourself with quality, performance and a style of your own. You do that and people will want your knives not someone elses knockoffs.
Good luck,
Rick