That's what I was dying to express (somewhat ineloquently, obviously) earlier. I think that the lead 121 in Glenderg's photo is in ST livery, the second is also in ST livery but has had the Tippex and IR 'points' logo added only.
I the previous photo 129 is probably also in ST livery with white additions, while 121 is likely a full respray in to 'proper' IR orange/tippex/IR points
I think I have only seen them on the right hand side of the locos and they may be on the other side of the lead 121. I might be wrong. Will try to look at some photos, and I have no idea what they were for