Paddy,
I think that I might have confused the issue with the link that I posted in #17.
When I joined Raleigh in the late 80's as a JS(O)2 the badge that was worn by us was the small shackle and spike badge.
In #16 you said that you saw the small shackle and marlin spike badge being worn on the right cuff by a Petty Officer. I posted the link in #17 because I was thought that perhaps that was the badge that you had seen, but I guess you missed it.
I posted the link in #18 because this was the first time that I had seen it in use.
Here is another link showing the Seaman Sub-Branch New Entrants badge being worn
http://www.youtube.com/watch?v=fc7eY63K8AI#t=120 It is smaller than the Seaman Specialist badge as I think can be seen from this video (I hope!).
I hope I am making myself a little clearer
There was a thread a while back with the suggestion of a more up to date version of the book by May, Carman & Tanner. I for one would welcome this and I would be more than willing to assist if I could, but I fear that my knowledge on Trade badges is limited. It wasn't until I joined this forum that I realised what a complicated subject it was!
Andy