Source: Guildmaster's Guide to Ravnica

Wondrous item, common

This thick, black paint is stored in a small jar, containing enough paint to apply moodmarks to one creature. The paint is dabbed on the face in spots or markings that often resemble the eyes of insects or spiders. Applying the paint in this way takes 1 minute.

For the next 8 hours, the marks change to reflect your mental state. A creature that can see you and makes a successful DC 10 Wisdom (Insight) check can discern whether you are happy, sad, angry, disgusted, surprised, or afraid, as well as the main source of that emotion. For example, you might communicate fear caused by a monster you just saw around the corner, grief at the loss of a friend, or happiness derived from pride in your performance in combat. A dark elf has advantage on this check.