I only sign when I remember to, but I normally don't. When I do, it depends on the size and it's use. If it's small I just use my initials and the year somewhere on the piece so if someone were to try to claim it, they would have to re-draw the place where I signed. If it's big and I don't really want a lot of people to use it (unless I give them permission) I use a program to add a watermark with a link to my dA profile.