Clear watermarks are a great way to protect your images, and at the same time not distract from what it is you are selling. This is a Photoshop tutorial, it is the program I most work in. Please be sure to click on the images if you need to zoom in.
1. Open your image. Hit Cntrl D to set your forground to black. Type out your Name (If you want a copyright symbol hit ALT 0169). Size it and position it where you think it looks best.
2. Rasterize your text by right-clicking on the layer in the layers palette and selecting rasterize.
4. To Smooth the edges, go to the Layers palette, turn on Lock Transparent Pixels (the first icon fron the left in the Lock section), and add a 2-3 pixel Gaussian Blur (Filter>Blur>Gaussian Blur).