Brothererekose wrote:
Any info on their iconography? What's the reason behind blue with scales? As opposed to
BA pretty-boys and their blood cups,
DAs' plains native american 'Thunderbird' rip-off iconography, etc.

The scales are a reference to the Hydra, the mythical beast who would regrow two heads for each one that was cut off. The Alpha Legion had a very decentralized command structure, as Alpharius trained his marines to think for themselves, discuss and off suggestions on all aspects of a military campaign, and to have multiple back-up plans in place.
Therefore, if one plan failed or an important leader was slain, the plan changed or someone else stepped up into command without missing a step.
Basically, the Alpha Legion are the Black Ops chapter, and have a penchant for complicated schemes, intrigue, and subterfuge, including impersonation of other chapters, using non-marine agents, and thinking outside the box. When they finally engage in combat, they like to have the deck stacked so much in their favor that victory is almost guaranteed.