The easiest and cheapest way to mark a single location with a component is just using a SceneComponent. It does not render in-game, but you can use its location and see it in the editor. Should be perfect for locations on a desk.
If, besides the location the direction also matters, then ArrowComponent is the way to go.
As another solution without components, you could make an InstanceEditable Vector array (or a single Vector if you need only one), and tick in the 3D widget checkbox in the details panel. It’ll place you gizmos for each array item, and update their values when you’re moving these.