Over in the Works in Progress forum, my most recent post revealed the Chapter Insignia - here I wanted to briefly explain my thinking behind it. 

There's two main things to point out from an 'in-universe' perspective - firstly, reflecting the Chapter's origin that they were intended as reinforcements for the Shadow Stalkers Chapter, there are echoes of their predecessors' Insignia. 

This symbol was named after the Eclipse of Strontium, the Ashen Sentinels retained the star/halo part to honour their fallen predecessors. 

Added to it is a skull, a familiar Warhammer motif  Here it represents memorial of those who have given their lives for the Emperor (also another nod to the Shadow Stalkers). It also represents a threat - death to the enemies of the Emperor; and it is a symbol of defiance - even if they burn their flesh, their bones will remain to watch over in judgement, a promise of future retribution. 

I think it tells their back story, is indicative of their outlook and temperament as a Chapter, and is suitably symbolic. Plus, it's typically Warhammer