A letter to Joseph Sloper dated 13th March 1868 represents the authority under which the perforation of postage stamps with initials was officially introduced.

Sloper's device/ideas were patented in 1858 so he had a monopoly on perfins from 1868 to 1872 when his patent rights ran out.
The first company to use perfins was COPESTAKE,MOORE, CRAMPTON & CO using the initials "S.C."
He was also granted permission to perforate Revenue Stamps with initials from 27th June 1870.