  The macroscopic signature for Weyl nodes so far has been the negative
longitudinal magnetoresistance arising from the chiral anomaly. However,
negative longitudinal magnetoresistance is not unique to chiral anomaly and can
arise due to completely different mechanisms such as current jetting or in
ferromagnetic systems due to the suppression of scattering with magnons.
Therefore, a macroscopic effect that can be uniquely attributed to the presence
of Weyl nodes is desirable. Here we show that the planar Hall effect could be a
hallmark for Weyl nodes. We investigated the anisotropic magnetoresistance and
planar Hall effect in Fe$_3$Sn$_2$, which has a kagome lattice and has been
predicted to be a type II Weyl metal. We discover that the planar Hall effect
contains a field antisymmetric contribution in addition to the ordinary field
symmetric contribution. The field antisymmetric planar Hall effect has a 3-fold
rotational symmetry, distinctively different from the symmetric planar Hall
effect, but consistent with the 3-fold rotational degeneracy of the
magnetization in Fe$_3$Sn$_2$. The temperature and field dependence of the
antisymmetric planar Hall effect rules out an interpretation based on
contribution from the anomalous Hall effect and is different from the symmetric
planar Hall effect, pointing to a different origin. We attribute the
antisymmetric planar Hall effect to the topological nature of Fe$_3$Sn$_2$ due
to the presence of Weyl II nodes. Our finding offers a promising route for
macroscopically probing Weyl systems.
