  Sulphur-bearing volatiles are observed to be significantly depleted in
interstellar and circumstellar regions. This missing sulphur is postulated to
be mostly locked up in refractory form. With ALMA we have detected sulphur
monoxide (SO), a known shock tracer, in the HD 100546 protoplanetary disk. Two
rotational transitions: $J=7_{7}-6_{6}$ (301.286 GHz) and $J=7_8-6_7$ (304.078
GHz) are detected in their respective integrated intensity maps. The stacking
of these transitions results in a clear 5$\sigma$ detection in the stacked line
profile. The emission is compact but is spectrally resolved and the line
profile has two components. One component peaks at the source velocity and the
other is blue-shifted by 5 km s$^{-1}$. The kinematics and spatial distribution
of the SO emission are not consistent with that expected from a purely
Keplerian disk. We detect additional blue-shifted emission that we attribute to
a disk wind. The disk component was simulated using LIME and a physical disk
structure. The disk emission is asymmetric and best fit by a wedge of emission
in the north east region of the disk coincident with a `hot-spot' observed in
the CO $J=3-2$ line. The favoured hypothesis is that a possible inner disk warp
(seen in CO emission) directly exposes the north-east side of the disk to
heating by the central star, creating locally the conditions to launch a disk
wind. Chemical models of a disk wind will help to elucidate why the wind is
particularly highlighted in SO emission and whether a refractory source of
sulphur is needed. An alternative explanation is that the SO is tracing an
accretion shock from a circumplanetary disk associated with the proposed
protoplanet embedded in the disk at 50 au. We also report a non-detection of SO
in the protoplanetary disk around HD 97048.
