The watermark appears only in the trial version of VEGAS Pro 15. It appears approximately 7½ seconds into the video you are editing.
In order to remove the watermark, you must purchase one of the three full versions of the software. The Edit version is the cheapest, but has the least amount of features. On the other end of the spectrum, the Suite version comes with all the bells and whistles, but it costs the most. (I myself got the Suite version mainly for NewBlue Titler Pro 5, an advanced 3D Text plug-in.)
But if you want a cheaper professional video editor, then I would recommend starting with VEGAS Movie Studio instead. I would say that the only major downside to this is that the number of video/audio tracks (how many video/audio clips you can have playing at the same time) is capped. For v14, it's capped at 10 for the cheapest option. Go to the next option up however and you have a very generous 200 track cap. (This is an upgrade from v13, as my Platinum Suite version has a cap of 20 video and 20 audio tracks.)
OK, being serious for a few nanoseconds, this flapping and flopping about by the sales and marketing of BOTH companies need to have their respective heads knocked together and discuss this with each other. Another example of Let the User/Customers sort it out. Outrageous behaviour all around. EndOfRant. 😎