Please be aware that you can adjust the watermark settings for your videos between a simple watermark in the upper right hand corner of your video or the full account URL in the bottom right of your video, however, this will not apply retroactively on older uploads. You will need to re-upload content if you would like the watermark to reflect your new settings.
The same applies if you change your username on the site. However, your old URL will forward to your new URL after a username change, so you won't be losing any traffic!
The watermark settings are also only applicable for videos, not photos. Photos will always have the bottom right corner watermark.