John Strype's Survey of the Cities of London and Westminster (1720) described the Society's Seal thus:
"It is the Representation of a Ship under full Sail, making up towards a Foreign Land; the Natives all about near the Shoar, with their Hands stretched out, or lifted up, and some on their Knees. A Minister in a Gown in the fore part of the Ship looking towards them, with the Gospel open in his Right Hand. And a Label in the middle of the Seal thus inscribed, TRANSIENS ADJUVA NOS: The Sun in the Firmament brightly shining out"The motto comes from the Acts of the Apostles 16:9, in which a vision of a man from Macedonia beseeches St Paul to 'come over and help us'.
The desire to save the immortal souls of the natives was not seen as in any way inconsistent with owning hundreds of slaves on the Barbados estate.
This stone version of the seal looks much older than 1907, the date of the SPG headquarters building designed by Sir William Emerson, where it now appears over the front door. Perhaps it was preserved from the original offices.
Emerson did contribute the statue in a niche on the corner of the building, which is of St Paul holding a closed book (his Epistles) and the sword with which he was martyred.
The SPG moved to Lambeth in 1987 and the Arts Council took it over, restructuring it and using the door in Great Peter Street as the main entrance. Above it, they carved their initials in stone - a rather nice touch considering the obvious thing to do would have been to get a thrusting modern designer to do a sign in chrome, neon and plexiglass.