I watermark all of my client work, but I don't watermark things I put on this forum. It is too distracting if I am looking for critique, or if I am trying to show my work. EVERYtHING I put on FB has my logo in the corner except images of my son, and snapshots. I have had images of my son stolen recently, someone was claiming them as their own, so I might start putting my logo on those too. My main reason for my logo is to advertise, and so that my clients PURCHASE the images and not just take them.