A follow-up to Ancestry Labs Beta February 27, 2019:
Add labels to people in your tree to highlight personal details or to clarify your research status. If you enable this feature, you will be able to access it directly from your tree and on every Facts page for the people in your tree.
It appears the tags will be visible to other people who view your tree from what people have reported. So you may want to be careful using certain tags (murderer, adultery, etc.) as some family members may take offense or even sue you for calling their ancestor a serial killer.
Here’s some more information from RootsTech: https://www.rootstech.org/video/what-you-dont-know-about-ancestry-crista-cowan (around 56:44 minutes long).