Source: Xanathar's Guide to Everything

Wondrous item, common (requires attunement)

This musical instrument has 3 charges. While you are playing it, you can use an action to expend 1 charge from the instrument and write a magical message on a nonmagical object or surface that you can see within 30 feet of you. The message can be up to six words long and is written in a language you know. If you are a bard, you can scribe an additional seven words and choose to make the message glow faintly, allowing it to be seen in nonmagical darkness. Casting Dispel Magic on the message erases it. Otherwise, the message fades away after 24 hours.

The instrument regains all expended charges daily at dawn.