Quick cheap good looking shadow box for medals.
Pickup a photo frame with deep sided (Walmart has them in dark colors)
Remove the glass.
Pickup some sticky backed "craft foam" (craft section at Walmart). Comes in all sorts of colors.
Use whatever colors strike your fancy, can get creative and use relevant branch flag colours, or go with plain black or whitr.
Use the removed glass as a template to trim the craft foam to fit into the frame with a sharp utility knife.
Remove the sticky backing, stick the foam to the cardboard backing in the photo frame.
Pin your medals, collar dogs, whatever, through the foam and put the pin backs on the back of the frame.
Easy to remove the medals to wear if you like as well.