I was the editor of Heels in 1980 & 81 when this logo first appeared. It was always a sheep perched on a peak with 'Baaa!' in a word-balloon coming from its mouth, and was scribbled by Peter Mansell in the margin of a trip report. I was unaware of the advertisement, and as he was a Hutt Valley lad I assume that he had spontaneously created it. I redrew it, & published it with the trip report, and it began being used after that in logbooks and Heels, & Baaa (which began publication in 1982 or thereabouts). I'm rather chuffed that it's still in use.