Magnetic impurities on the surface of Rashba spin-orbit-coupled, but otherwise conventional, superconductors provide a promising way to engineer topological superconductors with Majorana bound states as boundary modes. In this work we show that the spin-polarization in the interior of both one-dimensional impurity chains and two-dimensional islands in these systems can be used to determine the superconducting topological phase, as it changes sign exactly at the topological phase transition. Thus, spin polarization offers an alternative method to detect the topological phase in magnetic impurity chains and islands deposited on conventional superconductors, beyond the zero-energy Majorana bound states.