[zorg]

(First, I haven't been abducted, just trying to catch up).

I'd think that the Marines would prefer some logo with a martial bent, even though they're not trying to apply out traditional military solutions. If they have a motto (Duty is Honor, Honor is Sacrifice; or whatever, possibly in Latin), that could be added to the design (or choosen as a tattoo by the marines). Seeing that the sword is already taken, a skull motif might be a tad obvious, but still fitting (in the sense that they're courting death, and applying it - and, in the end, trying to prevent too much of it). Of course, skulls tend to go to the bad guys, so maybe not.

The Empire itself could use some sort of symbol for peace, or life, or security. A mailed fist with an olive branch? A dove in front of a shield? A burning sun in front of a tower? (I like the idea of the eagle grasping an olive branch and lightning bolts very much)
Again, an added motto (To serve Humanity; Duty from Fire; The Greatest Good) might be a good idea.