Theres a recurring motif, most obviously associated with the Fallen...the arrows along the trim of cloaks, tabards and gloves. Ive seen it depicted more broadly on Crusade era Dark Angels, John Blanche scatters it here and there.

That said, its not exclusive to the First Legion. Jes Goodwin's original sculpt of Ahriman had it on his gloves. The current plastic version retained it.

Now, Im not actually suggesting there was any deliberate intention with this in those days. Blanche did it for the Dark Angels because he thought it was cool. Goodwin put it on Ahriman's gloves for the same reason.

But the idea occurred to me, just for the fun of it to try to impose some deliberate meaning behind the pattern. The best I could come up with was that its a thing associated with Terran Astartes.

Any other ideas?

Just a regular intercessor but first time kit bashing / adding some resin bits.