The chance find of two bronze pennies with political graffiti added in white tipp-ex brought back vague memories of pirate radio in the North Sea. I was too young for the original story to register properly, but I do recall the navy raids on the transmitter ships in 1989. Ironically, the subsequent litigation confirmed that pirate radio had been ended by government piracy. The graffiti can be dated to sometime after 19 February 1967 with the formation of the Free Radio Association and its headline message ‘FIGHT FOR FREE RADIO’.
Numismatic Graffiti – End the BBC Monopoly – Fight for Free Radio – Gary Oddie
BNS Research Blog 
Thanks to Richard Kelleher at the Fitzwilliam Museum for bringing my attention to another specimen in the British Museum: https://www.britishmuseum.org/collection/object/C_2014-4152-3 is in the same hand, also with the curious ‘JF’ monogram. The reverse of that piece, a 1967 penny, is coloured blue and the writing in yellow.