The galley on fire, with the flames revealing a motif hidden within the galley head.
There’s a really good interview on BBC Radio Shetland’s Good Evening Shetland, 31st January 2018, where Guizer Jarl Stewart Jamieson and his wife Elanie talk about the day and mention the motif. Stewart’s father, the late Harry Jamieson, was Guizer Jarl in 1981 and the motif is from the design of the 1981 Jarl Squad shield. The motif was carved into the head by galley head builder Brydon Wright.
You can listen to the interview at: https://www.mixcloud.com/BBCShetland/good-evening-shetland-wednesday-31st-of-january-2018/
(interview starts at 25:46)