Somebody please explain a watermark and their purpose. Is it suppose to be present on a client's printed photo? I thought it would dissappear on prints.....? How do I manage a watermark so it's present on the digital files but not on the images when my clients want prints? Or as a professional photographer, specifically wedding, portraits, landscapes, etc., do I leave my watermark on prints for clients or whomever?
A watermark is some form of a logo (yours) that is suppose to let people know who took the photo, and/or to some what protect you from people taking your image. I can go on proof images that you send your clients so they don't just copy them and not pay you. Once you get paid, you can then print or give digital files to your clients without the water mark.
Lightroom doesn't apply the watermark to your original image...you slap it on during the export or print process as Chuck said to identify yourself and (try to) protect your image from someone being able to print them without paying you.
For proofs and stuff I send out, I'll sometimes slap on the watermark and also use the other export options to make a lower resolution and smaller version of the image that looks good on the web and for the client to see but not good enough to print or enlarge. If they put the image on Facebook, my watermark is visible. When they pay for the images, they get either clean, unwatermarked prints or digitial files.