The possibility of production of singlet Higgs particles coupling to exotic fermions at the CERN ${e}^{+}{e}^{\ensuremath{-}}$ Collider LEP or the SLAC Linear Collider through the loop-induced decay ${Z}^{0}\ensuremath{\rightarrow}{h}^{0}\ensuremath{\gamma}$ is discussed and decay signatures for the singlet Higgs boson are suggested. It appears that singlet Higgs bosons may be detectable with ${10}^{7}$ ${Z}^{0}'\mathrm{s}$, if the unknown masses and couplings are in the right range.