  Magnetic impurities on the surface of spin-orbit coupled but otherwise
conventional superconductors provide a promising way to engineer topological
superconductors with Majorana bound states as for boundary modes. In this work,
we show that the spin-polarization in the interior of both one-dimensional
impurity chains and two-dimensional islands can be used to determine the
topological phase, as it changes sign exactly at the topological phase
transition. This offers an independent probe of the topological phase, beyond
the zero-energy Majorana bound states appearing at the boundaries of the
topological region.
