You may not get it in PowerPoint Online. Also, you can add any watermark, including text, picture, shape, icon, 3D models, SmartArt, chart, etc. It is possible to insert images from online sources ...

or Powerpoint 2016 on your computer. Then select “New” file from a template you like to work with. If you do not have a 3D model or simply want to spice up your slides with a rotating globe ...