If you just want to let people know who did the sketch, then just put credits in the picture. It really irks me when people use the word "Copyright" on a piece of work he or she has done without knowing what it really is all about.
It's a mistake at best. At worst, it's perjury by saying you have copyrights to something you don't really have.
It's quite a stretch, I know, but I love big fancy words.
And by the way, please don't overreact to stuff. It makes you a drama queen, and believe me, it's not as cool as it sounds.