Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
SINKLER
As described in historical dictionaries
Patronymica Britannica (1860)
SINKLER. As vile a corruption of Sinclair, as Sinclair is of Saint Clair. Two London pork-butchers in 1852 bore the name,