There are a few things that separate a professional photographer or a serious photography business from amateur hobbyists and low-end professionals. If you haven't figured it out yet, the difference is in the little things, the details. Whether you know it or not, whenever you engage someone new, someone you may have a work interest in, your mind will automatically scan to find a few subtle signs to see if you're looking in the right place.
It's stuff like how you answer your phone and emails, how your website is designed and how your business card looks. All these things matter and they will also help you select the right kind of clientele. A good portfolio is obviously the starting point in creating a successful photography business, but being careful about these little things is also important.
One of the details that will be easily noticed by all your clients is your signature. The importance of a person's signature is one of those things that will stay the same no matter how much technology changes.
When it comes to watermarks, I personally prefer using my signature rather than a logo on my photos. Logos are cool for a website design and for larger businesses. A signature is something more personal and intimate and it gives clients the sense of something well crafted and high quality. Handwriting also looks better than the fonts most photographers use. I've seen some of the craziest logos for photography businesses, some of which had fonts from video games titles. If you're going to do that to yourself, have the common sense not to expect too much work coming your way.
If the signature watermark approach sounds interesting, check out this video posted Phlearn to learn how you can sign your photos and look like a true pro in the eyes of your clients.