Penny Black

Penny Black - world's first postage stamp was issued on 1st May 1840 in the UK, with the portrait of Queen Victoria. The idea of postage stamp was part of Sir Rowland Hill's 1837 proposals to reform the British postal system.

To commemorate the 150th anniversary of first postage stamp, Royal Mail had issued, during "Stamp World London 90" (International Stamp Exhibition in London, in 1990), a beautiful miniature sheet. The miniature sheet FDC is as shown above.

On the miniature sheet, also features Britannia riding the waves in triumph, in a chariot pulled by powerful horses, and holding a Union flag shield. The "Seahorse" design was based on several classical allusions, including Apollo and his sun chariot and imagery of Britannia from Roman and later British coinage.

I'm however not so sure what those letters "S" & "W" at the bottom left and right of the Penny Black mean ... ???