Currently, we do not have the option to automatically put a watermark into all your scenes. You may however easily do so by creating an image or text box with your watermark and editing its setting to a low opacity and without an opening and ending animation. This should also be placed first in the scene not after other assets. It would look like the screen recording below.
You can easily then proceed to duplicate the watermark and paste it in each scene.
Alternatively, you can upload a custom background that already has a backdrop with your company logo on it. This will ensure that it appears consistently across all scenes.