I /we believe they used WW2 style US army ranking system/patches. Gold on black
Attachment:
US-Army_1942-ranks.jpg [ 327.45 KiB | Viewed 1749 times ]
Ranks taken from PC roster match this system perfectly.
Attachment:
CAM00695.jpg [ 264.58 KiB | Viewed 1749 times ]
Per screen accuracy:
Privates - No insignia (see Frost, Crowe, and Ski. Drake had no sleeves anyways, but would not have had anything)
PFCs - single chevron on left arm (as seen on Spunkmeyer and Hudson's sleeve partially covered by roll. Vaz would presumably have had one if she had sleeves)
Corperals - double chevron on left sleeve (as seen on Ferro and Dietrich. Hicks presumably had one, but was not visible with high sleeve roll)
Master Seargent - Left sleeve as seen on Apone.
On a related note, regarding the "Delta" insignia vs. the Ship patch on the left breast pocket, screen accuracy indicates that Privates and PFCs wear the ship patch. Corporals and Sergeants wear the delta.
(mine below)
Attachment:
20150126_194132.jpg [ 2.89 MiB | Viewed 1747 times ]