Some helpful resources and rules of thumb for putting watermarks up on a smugmug pro account:
The concept and basic how to -
http://www.smugmug.com/help/custom-watermark-protection
A bit more detail -
http://dgrin.smugmug.com/gallery/1690196Tips: Make sure you keep the gif or the png SMALL! I set one up at 3000px wide and that was too large. The suggested (example) size for a watermark across a portrait orientation is "800x1200 or so". Make sure you upload the size you'd like to use as your watermark. I have small graphics on the corners of my images and uploaded ones that were 200 pixels wide max.
If you want the images to be transparent, stick with a gif or a png (24) file. And make sure you're saving a small one, and that image > mode > RGB color is set in Photoshop.
Hope that helps someone!
watermark in SmugMug
sign images in smugmug
put a brand on each smugmug image
size to upload watermark in smugmug
watermark won't upload in smugmug?