This disk is the third of the T1 “The Seasons” series, and I suppose this represents Autumn.
I can’t discern much detail here, and it looks a bit more like winter (ice, bare trees) than autumn… Is that a road at the right?
The single letter in the small triangle is “R”. The Spring disk has what looks like an “F”, and the Summer disk had an “i”. I’ll bet you 10 pence that the Winter disk has (when I find a photo of it) the letter “e”. “Fire” is promising, being a member of another set, the Four Elements, mentioned in the booklet.
I’m starting to like the way the designer of this Trail thinks.