  We describe the higher-form and non-invertible symmetries of 4d $\mathcal N=
3$ S-folds using the brane dynamics of their holographic duals. In cases with
enhancement to $\mathcal N=4$ supersymmetry, our analysis reproduces the known
field theory results of Aharony, Seiberg and Tachikawa, and is compatible with
the effective action recently given by Bergman and Hirano. Likewise, for two
specific $\mathcal N=3$ theories for which Zafrir has conjectured $\mathcal
N=1$ Lagrangians our results agree with those implied by the Lagrangian
description. In all other cases, our results imply novel predictions about the
symmetries of the corresponding $\mathcal N=3$ field theories.
