Credits:

YeahPotato

Step 1

Drag a New Signpost template from the map editor toolbar onto your map

Step 2

Change Kind to Hidden Item in the drop down menu

Step 3

Select and Item and Quantity

Step 4

Click + next to Hidden Item ID to assign a flag

Step 5

Generally, you will set the Elevation to 3 if the item is at "ground level"

Happy Hacking!