Watermarking your photographs is quite a controversial topic. Some people love them while others dispise them. It's one of the polarizing topics in photography.
Generally speaking I dislike watermarks on photographs but here are the best ways to watermark your photos:
Video by ProPhotoTips
Video by AnthonyMorganti
Learn more about watermarking on Wikipedia.
More photography videos.
More photography resources.
More photography articles.
Start learning photography today!