Point defects in chiral or particle–hole-symmetric crystals are topological objects: a vacancy in graphene binds a zero mode fixed by an index theorem, carrying a quantized, measurable charge. I will show how this topology is encoded in three places an experiment can reach: the displaced-state count, the scattering matrix, and the local density of states, and how an exact closed formula for the defect's scattering determinant yields a sum rule that distinguishes a true vacancy from a strong impurity. The same index structure governs interacting electrons bound to several defects, where the Coulomb interaction entangles the protected modes, and extends, unexpectedly, to the topological classification of two-qubit gates.