You misunderstood my 'why do you need one', there are clues in my answer to your online 'big sis'.
By questioning why you need one, you will either decide not to bother, or you'll decide exactly what it should look like.
Some watermarks are designed to prevent picture theft, some purely branding, some both. By working out your priorities you can design the best watermark for the job.
People often misinterpret answers like this to watermarks or websites as in some way arrogant. Thats miles off the truth, it's simply that most people haven't given enough thought to the options and their requirements.
OTOH it's the most common answer to the question 'recommend me a camera', and most people recognises it as helpful

.