Recent discoveries of black hole (BH) candidates in galactic and extragalactic globular clusters (GCs) have ignited interest in understanding how BHs dynamically evolve in a GC and the number of BHs (NBH) that may still be retained by today's GCs. Numerical models show that even if stellar-mass BHs are retained in today's GCs, they are typically in configurations that are not directly detectable. We show that a suitably defined measure of mass segregation (DELTA) between, e.g., giants and low-mass main-sequence stars, can be an effective probe to indirectly estimate NBH in a GC aided by calibrations from numerical models. Using numerical models including all relevant physics we first show that NBH is strongly anticorrelated with DELTA between giant stars and low-mass main-sequence stars. We apply the distributions of DELTA vs NBH obtained from models to three Milky Way GCs (47 Tuc, M 10, and M 22) known to contain stellar-mass BH candidates. For each GC, we calculate DELTA using publicly available ACS survey data taken by the Hubble space telescope. Using these observed DELTA and distributions of DELTA vs NBH from models as calibration, we predict distributions for NBH expected to be retained in these GCs. For 47 Tuc, M 10, and M 22, our predicted distributions peak at NBH ~ 8, 15, and 40, whereas, within the 2-sigma confidence level, NBH can be up to ~ 100, 50, and 200, respectively.