Photos with watermarks

Do you put your watermark on your photos?  I guess that's so if someone uses them on another site (besides yours) there's a reference to your name.  Credit maybe?

I've never done that, but it seems like a pretty good idea.

Unless you're trying for an artistic image, in which case it's like an intrusion into the design.

Maybe that's why I've steered clear.

But just in case I decide to do it, how do you do it? 
Is it just something in a camera, or when I download onto the computer, or do I have to add it as an editing tool?

I'm willing to learn.  I may even try doing it.  Let me know if you have the skills...Thanks.