Radio Caroline returned to the air in September 1972 from the MV Mi Amigoand the publicity material gradually evolved over the rest of the decade to reflect the changes in format, the move to become an album oriented station and the split frequencies used for the Dutch and English services.
An ingenious play on wording was used to circumvent the (particularly British) legislation outlawing offshore radio broadcasting.
These stickers apparently warned listeners that it was illegal to listen to the station, but also managed to convey the necessary information (wavelength) enabling them to do so.