They’re signs that guide the witch along her path.
Since their heads look like brains, you’d think that they’re well-informed about geography, but since they have no idea where the witch’s homeland is, they always just point in some random direction. In fact, they can’t even tell which cardinal direction is which.
This Minion provides the Witch with directions. Its head looks very much like a brain, so one would think it is familiar with the lay of the land. However, it does not know where its Witch's hometown is, so it simply points in the first direction that comes to mind. In fact, it does not even differentiate between north, south, east, or west.