Wondrous item, common
The stick will make about thirty marks before it is used up, each no larger than a hand's breadth. A mark you make is plainly visible to you and cannot be seen by any other creature, nor by any magic that reveals writing, nor through truesight. It shows through whitewash, tar, pitch, and paint.
You know the direction and the distance of the nearest of your own marks within 1 mile, whether or not you can see it. A mark lasts until the stick that made it is used up or destroyed, and then all its marks go at once.
The chalk knows nothing of what the marks mean. Grauwe's marks are on the doors of this city yet, and the stick is here on the table.
Source: Provenance — The Quist Sale