Here are the last two Mantis Warriors that I have to paint at the moment. The first is my Captain. I'll be fielding him with a relic blade, represented by the Kromlech vibro-katana.
Here's the Captain's banner. I used the quartered pattern that's standard for 5th companies. I tried to make this banner more complex, painting different designs on each side. While I like the look of the more complicated Mantis design in the second photo, I don't think it stands out well enough against the green, despite some extra highlighting in an attempt to make it pop.
Lastly, here's my other Sergeant. He's another of the official White Scar models.
He has another complex banner, though not as complex as the Captain's. I painted this banner yellow, and I was really happy with the look of it. It contrasts against the armor and the black design on it, but still fits with the model as a whole. The same design is painted on both sides.
That's it for the Mantis Warriors for the moment. Next up will be some more Executioners.