  A visible action on a complex manifold is a holomorphic action that admits a
$J$-transversal totally real submanifold $S$.
  It is said to be strongly visible if there exists an orbit-preserving
anti-holomorphic diffeomorphism $\sigma$ such that $\sigma |_S = \mathrm{id}$.
  In this paper, we prove that for any Hermitian symmetric space $D = G/K$ the
action of any symmetric subgroup $H$ is strongly visible.
  The proof is carried out by finding explicitly an orbit-preserving
anti-holomorphic involution and a totally real submanifold $S$.
  Our geometric results provide a uniform proof of various multiplicity-free
theorems of irreducible highest weight modules when restricted to reductive
symmetric pairs, for both classical and exceptional cases, for both finite and
infinite dimensional cases, and for both discrete and continuous spectra.
