Do you mean in paper print form? Or digital files?
Digital files, I don't worry about it. They're all at "web resolution," and you can't get a decent print of any size from the images I post. I've yet to find one of my digitized photos on someone else's website, so it simply hasn't been an issue. I did, at one time, include an unobtrusive but clear copyright notice near the edge of the image, but I typically don't bother anymore.
With paper prints, I write a few things on the back... copyright notice, my name, and print/negative ID (mainly so I can make another one later... I log all my printing information). I do this with a #2 graphite pencil in small letters near the edge on the back of the print, being careful not to leave an imprint that goes through the paper.
Normally, though, I just don't distribute paper prints. Haven't had much need to do so.