The Sergeant (Chris Obi) has a mixture of ribbons from the Air Force Basic Training Ribbon (on top row for God's sake) to the Bronze Star (on the position of the least ranking -- it is the 20th military ranking of all military awards and is usually found on the top (highest ranking) row.
There are other service and auxiliary ribbons that could be from JrROTC to Police/Fire to Foreign.
All it takes for wardrobe to set these ribbons correctly is to look up the proper military service "Order of Preference."