Want to see the build number at a glance on your every-day device? On your Slow Ring Insider build whether or not a preview has flighted yet in the current cycle?
You can toggle the watermark on and off using regedit or a third-party utility. You can show the watermark on any build in any edition. The registry key is here: (1 = on, 0 = off)
Close regedit and restart. Best practice is to export the registry key to your desktop before you make any changes so you can recover easily if you mess up. Name the exported key appropriately. After you make the change, export again and name that appropriately. You now have an easy way to toggle the watermark on and off.
If you are hesitant to use regedit, you can use a third-party utility. I like Ultimate Windows Tweaker 4.3. The checkbox for this feature is here:
I am not recommending this free app. Just showing how I use it to show or hide the watermark if I don't feel like using regedit or want to also change some other attribute.