This one was about for many years. It consisted of a plaintive, endless mewing sound which frequented the high 8 MHz or low 9 MHz area of the bands, and was caused by a slowly sweeping carrier.
Four transmissions always operated in two parallel pairs, each pair exactly 110 kHz apart. Pairs were not related, but were always at least 110 kHz away from each other.
Signals were usually weak in the UK, but audible 24 hrs a day. with the BFO switched on, and careful tuning was necessary.
No reports of this signal have been received for at least ten years, so it is believed transmissions have ceased.