I'm working with Lightroom CC 2015.1 and Lighroom mobile and Adobe Slate. When adding Photos from Lightroom mobile into Adobe Slate: Ist it possible to have a watermark on every picture. I found no way to have watermarks added without first exporting in Lightroom CC into e.g. jpg.
It's not possible to watermark raw images. If your originals are proprietary raw files or DNG you would need to export e.g. a tiff, PSD or jpeg with the watermark. Then create a sync'd collection with the exported copies.