The debate over watermarks has been going on ever since digital photography got married to forums and chat rooms. Everybody has an opinion on watermarks, but generally, they are divided into 2 sides. The first side thinks that watermarks are useful because they protect photos from being stolen on the Internet and other mediums, while the other side thinks watermarks are for wannabe artists who want to look more important than they really are.
(Success Tip: Get a new photo idea every day.)
If you're hoping I'm going to choose sides, I will have to disappoint you. This is not about watermarks being right or wrong. One undeniable truth about them though is that they can be useful. A watermarked image will deliver your name with it and it will associate something good looking with an identity.
It can be an efficient tool in marketing a photography business, but one that has to be used carefully and with common sense. A watermark should be small rather than large. It should be visible but without stealing attention away from the actual photograph or making it difficult to view. There are plenty of "not this way" examples on the web. Trust your good judgment when using watermarks. Ultimately, you'll be the one to win or lose.
Meanwhile, Aaron Nace from Phlearn has a great video showing you the best way to watermark your photos. We highly recommended it.