Primordial black holes endowed with magnetic charges may circumvent the constraints imposed by Hawking radiation, enabling the existence of their substantial populations even for masses below \(10^{15}\,\textrm{g}\) . In this study, we examine their distinct Faraday rotation signatures and establish new Parker-type constraints on their abundance. These findings restrict the dark matter fraction in primordial magnetic black holes, using intergalactic magnetic fields in cosmic voids to \(f_{{ DM}} \lesssim 10^{-8}\) and in cosmic web filaments to \(f_{{ DM}} \lesssim 10^{-4}\) . Additionally, extremal primordial magnetic black holes with masses \(M^{{ ex.}}_{{ BH}}\gtrsim 10^{-6}~{M}_\odot \) produce observable shifts in polarization angle and rotation measure values. This effect exceeds associated with neutron stars such as Magnetars with comparable magnetic fields.